Hi,
Is it possible to dynamically change enumeration list of DRM enumeration property ? Motivation behind this question is to understand whether it is possible to create connector enum property (e.g a property which will list supported output encodings - like yuv420, yuv422 etc) whose list of supported enum values could be changed dynamically e.g. based on which sink is connected.
I think there is existing EDID connector property whose value changes based on connected sink. EDID is a BLOB property, I am trying to understand if this is also possible for ENUM type property. There is "drm_property_replace_blob" to replace blob but I wasn't able to find any API which could replace list of supported enums. Alternatively, would it be good idea to destroy custom enum property created by a driver and create new enum property with new list of supported enums e.g when there is a HOTPLUG event.
Thanks, -Yogish
On Tue, May 26, 2020 at 6:31 AM Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
Is it possible to dynamically change enumeration list of DRM enumeration property ? Motivation behind this question is to understand whether it is possible to create connector enum property (e.g a property which will list supported output encodings - like yuv420, yuv422 etc) whose list of supported enum values could be changed dynamically e.g. based on which sink is connected.
I think there is existing EDID connector property whose value changes based on connected sink. EDID is a BLOB property, I am trying to understand if this is also possible for ENUM type property. There is "drm_property_replace_blob" to replace blob but I wasn't able to find any API which could replace list of supported enums. Alternatively, would it be good idea to destroy custom enum property created by a driver and create new enum property with new list of supported enums e.g when there is a HOTPLUG event.
Neither works, properties and their value ranges are static. Also generally the idea is that the properties on the drm_connector reflect what the source side can do, irrespective of the sink capabilities. Since a lot of sinks have bad EDID and you might want to overwrite what the sink claims works.
Usually how we do this is a second property that the kernel sets, and userspace can only read, which shows what the sink is capable of. Sometimes we also just let userspace re-decode the EDID and figure that out itself, but that's kinda a bad interface.
Also for anything new, please keep in mind our rules for new uapi: https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#open-source-userspace... https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#testing-and-validatio...
Cheers, Daniel
-Daniel
On Tue, 26 May 2020 10:01:23 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
Is it possible to dynamically change enumeration list of DRM enumeration property ? Motivation behind this question is to understand whether it is possible to create connector enum property (e.g a property which will list supported output encodings - like yuv420, yuv422 etc) whose list of supported enum values could be changed dynamically e.g. based on which sink is connected.
I think there is existing EDID connector property whose value changes based on connected sink. EDID is a BLOB property, I am trying to understand if this is also possible for ENUM type property. There is "drm_property_replace_blob" to replace blob but I wasn't able to find any API which could replace list of supported enums. Alternatively, would it be good idea to destroy custom enum property created by a driver and create new enum property with new list of supported enums e.g when there is a HOTPLUG event.
Hi,
looking at Weston code, it *might* cope with it. A hotplug event does cause Weston to re-discover all properties of a connector. This is specific to connectors only.
The race exists though: userspace might be poking at KMS after you changed the property in the kernel but before userspace handles the hotplug event. You'd have to check that does not cause regressions. I guess for a completely new property, the risk seems low, as userspace does not know to poke at it (risk of using outdated property or value IDs causing unexpected atomic commit failure). Also I'm not aware of any KMS program that would yet attempt blind KMS state save & restore to sanitize the KMS state after dropping and re-gaining DRM master.
You'd have to check all other KMS using programs too: every Wayland compositor, Xorg, DRM Vulkan WSI(?), ...
Thanks, pq
Thanks, Daniel & Pekka.
It might be bad idea to destroy and re-create the connector enum property from HOTPLUG handler in DRM. But if this is done through DRM_IOCTL_MODE_GETCONNECTOR, there won't be race, right ? From code walk through it seems that Weston will call this IOCTL for newly connected display found through HOTPLUG event and DRM driver will update the EDID through the call sequence triggered by this IOCTL. On the similar line if existing connector property is destroyed and re-created with new enmu list through this IOCTL call chain, then there won't be race ?
Thanks, -Yogish
On Tue, May 26, 2020 at 1:09 PM Pekka Paalanen ppaalanen@gmail.com wrote:
On Tue, 26 May 2020 10:01:23 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
Is it possible to dynamically change enumeration list of DRM enumeration property ? Motivation behind this question is to understand whether it is possible to create connector enum property (e.g a property which will
list
supported output encodings - like yuv420, yuv422 etc) whose list of supported enum values could be changed dynamically e.g. based on which
sink
is connected.
I think there is existing EDID connector property whose value changes
based
on connected sink. EDID is a BLOB property, I am trying to understand if this is also possible for ENUM type property. There is "drm_property_replace_blob" to replace blob but I wasn't able to find any API which could replace list of supported enums. Alternatively, would it
be
good idea to destroy custom enum property created by a driver and create new enum property with new list of supported enums e.g when there is a HOTPLUG event.
Hi,
looking at Weston code, it *might* cope with it. A hotplug event does cause Weston to re-discover all properties of a connector. This is specific to connectors only.
The race exists though: userspace might be poking at KMS after you changed the property in the kernel but before userspace handles the hotplug event. You'd have to check that does not cause regressions. I guess for a completely new property, the risk seems low, as userspace does not know to poke at it (risk of using outdated property or value IDs causing unexpected atomic commit failure). Also I'm not aware of any KMS program that would yet attempt blind KMS state save & restore to sanitize the KMS state after dropping and re-gaining DRM master.
You'd have to check all other KMS using programs too: every Wayland compositor, Xorg, DRM Vulkan WSI(?), ...
Thanks, pq
On Tue, May 26, 2020 at 9:39 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Tue, 26 May 2020 10:01:23 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
Is it possible to dynamically change enumeration list of DRM enumeration property ? Motivation behind this question is to understand whether it is possible to create connector enum property (e.g a property which will list supported output encodings - like yuv420, yuv422 etc) whose list of supported enum values could be changed dynamically e.g. based on which sink is connected.
I think there is existing EDID connector property whose value changes based on connected sink. EDID is a BLOB property, I am trying to understand if this is also possible for ENUM type property. There is "drm_property_replace_blob" to replace blob but I wasn't able to find any API which could replace list of supported enums. Alternatively, would it be good idea to destroy custom enum property created by a driver and create new enum property with new list of supported enums e.g when there is a HOTPLUG event.
Hi,
looking at Weston code, it *might* cope with it. A hotplug event does cause Weston to re-discover all properties of a connector. This is specific to connectors only.
Currently the kernel doesn't cope with that. Only objects which can be added/removed are connectors, blobs and fbs (iow the refcounted ones). Adding/removing properties isn't supported, nor is adding/removing which properties are attached to which object while that object is life.
Also I think the uapi risk for this is way too big, see my other reply for what we've done in the past for stuff like this. -Daniel
The race exists though: userspace might be poking at KMS after you changed the property in the kernel but before userspace handles the hotplug event. You'd have to check that does not cause regressions. I guess for a completely new property, the risk seems low, as userspace does not know to poke at it (risk of using outdated property or value IDs causing unexpected atomic commit failure). Also I'm not aware of any KMS program that would yet attempt blind KMS state save & restore to sanitize the KMS state after dropping and re-gaining DRM master.
You'd have to check all other KMS using programs too: every Wayland compositor, Xorg, DRM Vulkan WSI(?), ...
Thanks, pq _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
For creating new source property, is it good to follow "drm_mode_create_hdmi_colorspace_property()" as an example ? It seems that currently there is no standard DRM property which allows DRM client to set a specific output encoding (like YUV420, YUV422 etc). Also, there is no standard property for letting client select YUV/RGB color range. I see there are two ways to introduce new properties, 1. do something like drm_mode_create_hdmi_colorspace_property 2. create custom property similar to "Broadcast RGB". Is there opinion on which is a preferable way to expose encoding and color rage selection property ?
Thanks, -Yogish
On Tue, May 26, 2020 at 5:44 PM Daniel Vetter daniel@ffwll.ch wrote:
On Tue, May 26, 2020 at 9:39 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Tue, 26 May 2020 10:01:23 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
Is it possible to dynamically change enumeration list of DRM
enumeration
property ? Motivation behind this question is to understand whether it
is
possible to create connector enum property (e.g a property which will
list
supported output encodings - like yuv420, yuv422 etc) whose list of supported enum values could be changed dynamically e.g. based on which
sink
is connected.
I think there is existing EDID connector property whose value changes
based
on connected sink. EDID is a BLOB property, I am trying to understand
if
this is also possible for ENUM type property. There is "drm_property_replace_blob" to replace blob but I wasn't able to find
any
API which could replace list of supported enums. Alternatively, would
it be
good idea to destroy custom enum property created by a driver and
create
new enum property with new list of supported enums e.g when there is a HOTPLUG event.
Hi,
looking at Weston code, it *might* cope with it. A hotplug event does cause Weston to re-discover all properties of a connector. This is specific to connectors only.
Currently the kernel doesn't cope with that. Only objects which can be added/removed are connectors, blobs and fbs (iow the refcounted ones). Adding/removing properties isn't supported, nor is adding/removing which properties are attached to which object while that object is life.
Also I think the uapi risk for this is way too big, see my other reply for what we've done in the past for stuff like this. -Daniel
The race exists though: userspace might be poking at KMS after you changed the property in the kernel but before userspace handles the hotplug event. You'd have to check that does not cause regressions. I guess for a completely new property, the risk seems low, as userspace does not know to poke at it (risk of using outdated property or value IDs causing unexpected atomic commit failure). Also I'm not aware of any KMS program that would yet attempt blind KMS state save & restore to sanitize the KMS state after dropping and re-gaining DRM master.
You'd have to check all other KMS using programs too: every Wayland compositor, Xorg, DRM Vulkan WSI(?), ...
Thanks, pq _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
-- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch
On Thu, May 28, 2020 at 12:29:43PM +0530, Yogish Kulkarni wrote:
For creating new source property, is it good to follow "drm_mode_create_hdmi_colorspace_property()" as an example ? It seems that currently there is no standard DRM property which allows DRM client to set a specific output encoding (like YUV420, YUV422 etc). Also, there is no standard property for letting client select YUV/RGB color range. I see there are two ways to introduce new properties, 1. do something like drm_mode_create_hdmi_colorspace_property 2. create custom property similar to "Broadcast RGB". Is there opinion on which is a preferable way to expose encoding and color rage selection property ?
I guess first question is "why?" Thus far we've gone with the opinion that automatically configuring output stuff as much as possible is best. What's the use-case where the driver can't select this? -Daniel
Thanks, -Yogish
On Tue, May 26, 2020 at 5:44 PM Daniel Vetter daniel@ffwll.ch wrote:
On Tue, May 26, 2020 at 9:39 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Tue, 26 May 2020 10:01:23 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
Is it possible to dynamically change enumeration list of DRM
enumeration
property ? Motivation behind this question is to understand whether it
is
possible to create connector enum property (e.g a property which will
list
supported output encodings - like yuv420, yuv422 etc) whose list of supported enum values could be changed dynamically e.g. based on which
sink
is connected.
I think there is existing EDID connector property whose value changes
based
on connected sink. EDID is a BLOB property, I am trying to understand
if
this is also possible for ENUM type property. There is "drm_property_replace_blob" to replace blob but I wasn't able to find
any
API which could replace list of supported enums. Alternatively, would
it be
good idea to destroy custom enum property created by a driver and
create
new enum property with new list of supported enums e.g when there is a HOTPLUG event.
Hi,
looking at Weston code, it *might* cope with it. A hotplug event does cause Weston to re-discover all properties of a connector. This is specific to connectors only.
Currently the kernel doesn't cope with that. Only objects which can be added/removed are connectors, blobs and fbs (iow the refcounted ones). Adding/removing properties isn't supported, nor is adding/removing which properties are attached to which object while that object is life.
Also I think the uapi risk for this is way too big, see my other reply for what we've done in the past for stuff like this. -Daniel
The race exists though: userspace might be poking at KMS after you changed the property in the kernel but before userspace handles the hotplug event. You'd have to check that does not cause regressions. I guess for a completely new property, the risk seems low, as userspace does not know to poke at it (risk of using outdated property or value IDs causing unexpected atomic commit failure). Also I'm not aware of any KMS program that would yet attempt blind KMS state save & restore to sanitize the KMS state after dropping and re-gaining DRM master.
You'd have to check all other KMS using programs too: every Wayland compositor, Xorg, DRM Vulkan WSI(?), ...
Thanks, pq _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
-- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch
I am trying to find a way through Weston which will allow setting specific encoding at display output. Could you please elaborate on why it is best to let DRM driver automatically configure which encoding to choose rather than making it selectable by DRM client ? I am not able to find reference to past discussion about this. I was only able to find a proposed change - https://lists.freedesktop.org/archives/intel-gfx/2017-April/125451.html but am not able to find why it got rejected.
Alternatively, is there existing way through which DRM clients can specify preference for output encoding ? Or currently it's all up to the DRM driver to choose what output encoding to use.
Thanks, -Yogish
On Thu, May 28, 2020 at 1:54 PM Daniel Vetter daniel@ffwll.ch wrote:
On Thu, May 28, 2020 at 12:29:43PM +0530, Yogish Kulkarni wrote:
For creating new source property, is it good to follow "drm_mode_create_hdmi_colorspace_property()" as an example ? It seems
that
currently there is no standard DRM property which allows DRM client to
set
a specific output encoding (like YUV420, YUV422 etc). Also, there is no standard property for letting client select YUV/RGB color range. I see there are two ways to introduce new properties, 1. do something like drm_mode_create_hdmi_colorspace_property 2. create custom property
similar
to "Broadcast RGB". Is there opinion on which is a preferable way to
expose
encoding and color rage selection property ?
I guess first question is "why?" Thus far we've gone with the opinion that automatically configuring output stuff as much as possible is best. What's the use-case where the driver can't select this? -Daniel
Thanks, -Yogish
On Tue, May 26, 2020 at 5:44 PM Daniel Vetter daniel@ffwll.ch wrote:
On Tue, May 26, 2020 at 9:39 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Tue, 26 May 2020 10:01:23 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
Is it possible to dynamically change enumeration list of DRM
enumeration
property ? Motivation behind this question is to understand
whether it
is
possible to create connector enum property (e.g a property which
will
list
supported output encodings - like yuv420, yuv422 etc) whose list
of
supported enum values could be changed dynamically e.g. based on
which
sink
is connected.
I think there is existing EDID connector property whose value
changes
based
on connected sink. EDID is a BLOB property, I am trying to
understand
if
this is also possible for ENUM type property. There is "drm_property_replace_blob" to replace blob but I wasn't able to
find
any
API which could replace list of supported enums. Alternatively,
would
it be
good idea to destroy custom enum property created by a driver and
create
new enum property with new list of supported enums e.g when there
is a
HOTPLUG event.
Hi,
looking at Weston code, it *might* cope with it. A hotplug event does cause Weston to re-discover all properties of a connector. This is specific to connectors only.
Currently the kernel doesn't cope with that. Only objects which can be added/removed are connectors, blobs and fbs (iow the refcounted ones). Adding/removing properties isn't supported, nor is adding/removing which properties are attached to which object while that object is life.
Also I think the uapi risk for this is way too big, see my other reply for what we've done in the past for stuff like this. -Daniel
The race exists though: userspace might be poking at KMS after you changed the property in the kernel but before userspace handles the hotplug event. You'd have to check that does not cause regressions. I guess for a completely new property, the risk seems low, as userspace does not know to poke at it (risk of using outdated property or value IDs causing unexpected atomic commit failure). Also I'm not aware of any KMS program that would yet attempt blind KMS state save & restore to sanitize the KMS state after dropping and re-gaining DRM master.
You'd have to check all other KMS using programs too: every Wayland compositor, Xorg, DRM Vulkan WSI(?), ...
Thanks, pq _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
-- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch
-- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
On Thu, 28 May 2020 17:38:59 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
I am trying to find a way through Weston which will allow setting specific encoding at display output.
Hi,
why do *you* want to control that?
Why not let the driver always choose the highest possible encoding given the video mode and hardware capability?
I can understand userspace wanting to know what it got, but why should userspace be able to control it?
Would people want to pick the encoding first, and then go for the highest possible video mode?
Could you please elaborate on why it is best to let DRM driver automatically configure which encoding to choose rather than making it selectable by DRM client ? I am not able to find reference to past discussion about this. I was only able to find a proposed change - https://lists.freedesktop.org/archives/intel-gfx/2017-April/125451.html but am not able to find why it got rejected.
Alternatively, is there existing way through which DRM clients can specify preference for output encoding ? Or currently it's all up to the DRM driver to choose what output encoding to use.
There must be some reason why userspace needs to be able to control it. I'm also asking as a Weston maintainer, since I'm interested in how this affects e.g. color reproduction or HDR support.
One thing that comes to my mind is using atomic TEST_ONLY commits to probe all the possible video modes × encodings for presenting a list to the user to choose from, if you have a display configuration GUI. E.g with some TV use cases, maybe the user wants to avoid sub-sampling, use the native resolution, but limit refresh rate to what's actually possible. Or any other combination of the three.
Thanks, pq
Thanks, -Yogish
On Thu, May 28, 2020 at 1:54 PM Daniel Vetter daniel@ffwll.ch wrote:
On Thu, May 28, 2020 at 12:29:43PM +0530, Yogish Kulkarni wrote:
For creating new source property, is it good to follow "drm_mode_create_hdmi_colorspace_property()" as an example ? It seems
that
currently there is no standard DRM property which allows DRM client to
set
a specific output encoding (like YUV420, YUV422 etc). Also, there is no standard property for letting client select YUV/RGB color range. I see there are two ways to introduce new properties, 1. do something like drm_mode_create_hdmi_colorspace_property 2. create custom property
similar
to "Broadcast RGB". Is there opinion on which is a preferable way to
expose
encoding and color rage selection property ?
I guess first question is "why?" Thus far we've gone with the opinion that automatically configuring output stuff as much as possible is best. What's the use-case where the driver can't select this? -Daniel
Hi,
For letting DRM clients to select output encoding: Sink can support certain display timings with high output bit-depths using multiple output encodings, e.g. sink can support a particular timing with RGB 10-bit, YCbCr422 10-bit and YCbCr420 10-bit. So DRM client may want to select YCbCr422 10-bit over RBG 10-bit output to reduce the link bandwidth (and in turn reduce power/voltage). If DRM driver automatically selects output encoding then we are restricting DRM clients from making appropriate choice.
For selectable output color range: Certain applications (typically graphics) usually rendered in full range while some applications (typically video) have limited range content. Since content can change dynamically, DRM driver does not have enough information to choose correct quantization. Only DRM client can correctly select which quantization to set (to preserve artist's intent).
For how to use selectable output encoding with Weston: I was thinking that DRM should have separate property to list the encodings supported by sink and Weston will present this list to its client. Your idea to validate encodings using TEST_ONLY commit and present a list of timings along with encodings supported by particular timing seems better. Instead of validating all possible encodings, does it make sense to validate only those supported by sink? Irrespective of this we would anyway need some mechanism which will allow user to select particular encoding for a particular mode. I was thinking to allow this using new DRM property "Encoding". Do you have anything better in mind?
(Since I am using my Gmail Id, I feel I should mention that I work at Nvidia)
Thanks, -Yogish
On Thu, May 28, 2020 at 6:18 PM Pekka Paalanen ppaalanen@gmail.com wrote:
On Thu, 28 May 2020 17:38:59 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
I am trying to find a way through Weston which will allow setting
specific
encoding at display output.
Hi,
why do *you* want to control that?
Why not let the driver always choose the highest possible encoding given the video mode and hardware capability?
I can understand userspace wanting to know what it got, but why should userspace be able to control it?
Would people want to pick the encoding first, and then go for the highest possible video mode?
Could you please elaborate on why it is best to let DRM driver automatically configure which encoding to choose rather than making it selectable by DRM client ? I am not able to find reference to past discussion about this. I was only able to find a proposed change
https://lists.freedesktop.org/archives/intel-gfx/2017-April/125451.html
but
am not able to find why it got rejected.
Alternatively, is there existing way through which DRM clients can
specify
preference for output encoding ? Or currently it's all up to the DRM
driver
to choose what output encoding to use.
There must be some reason why userspace needs to be able to control it. I'm also asking as a Weston maintainer, since I'm interested in how this affects e.g. color reproduction or HDR support.
One thing that comes to my mind is using atomic TEST_ONLY commits to probe all the possible video modes × encodings for presenting a list to the user to choose from, if you have a display configuration GUI. E.g with some TV use cases, maybe the user wants to avoid sub-sampling, use the native resolution, but limit refresh rate to what's actually possible. Or any other combination of the three.
Thanks, pq
Thanks, -Yogish
On Thu, May 28, 2020 at 1:54 PM Daniel Vetter daniel@ffwll.ch wrote:
On Thu, May 28, 2020 at 12:29:43PM +0530, Yogish Kulkarni wrote:
For creating new source property, is it good to follow "drm_mode_create_hdmi_colorspace_property()" as an example ? It
seems
that
currently there is no standard DRM property which allows DRM client
to
set
a specific output encoding (like YUV420, YUV422 etc). Also, there is
no
standard property for letting client select YUV/RGB color range. I
see
there are two ways to introduce new properties, 1. do something like drm_mode_create_hdmi_colorspace_property 2. create custom property
similar
to "Broadcast RGB". Is there opinion on which is a preferable way
to
expose
encoding and color rage selection property ?
I guess first question is "why?" Thus far we've gone with the opinion
that
automatically configuring output stuff as much as possible is best.
What's
the use-case where the driver can't select this? -Daniel
On Mon, 1 Jun 2020 09:22:27 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
For letting DRM clients to select output encoding: Sink can support certain display timings with high output bit-depths using multiple output encodings, e.g. sink can support a particular timing with RGB 10-bit, YCbCr422 10-bit and YCbCr420 10-bit. So DRM client may want to select YCbCr422 10-bit over RBG 10-bit output to reduce the link bandwidth (and in turn reduce power/voltage). If DRM driver automatically selects output encoding then we are restricting DRM clients from making appropriate choice.
Hi,
right, that seems to be another reason.
For selectable output color range: Certain applications (typically graphics) usually rendered in full range while some applications (typically video) have limited range content. Since content can change dynamically, DRM driver does not have enough information to choose correct quantization. Only DRM client can correctly select which quantization to set (to preserve artist's intent).
Now this is an interesting topic for me. As far as I know, there is no window system protocol to tell the display server whether the application provided content is using full or limited range. This means that the display server cannot tell DRM about full vs. limited range either. It also means that when not fullscreen, the display server cannot show the limited range video content correctly, because it would have to be converted to full-range (or vice versa).
But why would an application produce limited range pixels anyway? Is it common that hardware video decoders are unable to produce full-range pixels?
I am asking, because I have a request to add limited vs. full range information to Wayland.
What about video sinks, including monitors? Are there devices that accept limited-range only, full-range only, or switchable?
Why not just always use full-range everywhere?
Or if a sink supports only limited-range, have the display chip automatically convert from full-range, so that software doesn't have to convert in software.
If you actually have a DRM KMS property for the range, does it mean that: - the sink is configured to accept that range, and the pixels in the framebuffer need to comply, or - the display chip converts to that range while framebuffer remains in full-range?
If we look at I915 driver's "Broadcast RGB" property, it seems to say to me that the framebuffer is always primarily assumed to be in full-range, and the conversion to limited-range happens in the scanout circuitry. So that property would not help with video content that is already in limited-range.
To recap, there are two orthogonal things: application content or framebuffer range, and video sink / monitor range. The display server between the two, at last if it is a Wayland compositor, would be able to convert as necessary.
For how to use selectable output encoding with Weston: I was thinking that DRM should have separate property to list the encodings supported by sink and Weston will present this list to its client. Your
Not client. A configuration tool perhaps, but not generically to all Wayland clients, not as a directly settable knob at least.
idea to validate encodings using TEST_ONLY commit and present a list of timings along with encodings supported by particular timing seems better. Instead of validating all possible encodings, does it make sense to validate only those supported by sink? Irrespective of this we would
Yes, having a list of what the sink actually supports would be nice.
As for Wayland clients, there is an extension brewing at https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/8 that would allow suggesting the optimal encoding (pixel format and modifier really) in flight.
That said, we are talking about the two different things here: framebuffer format vs. encoding on the wire. Whether making them match has benefits is another matter.
anyway need some mechanism which will allow user to select particular encoding for a particular mode. I was thinking to allow this using new DRM property "Encoding". Do you have anything better in mind?
I think that is a reasonable and useful goal and idea. Just remember to document it when proposing, even if it seems obvious. The details on how to formulate that into UAPI is up for debate.
As said, changing KMS properties after they have been exposed to userspace won't really work from either kernel or userspace point of view. So you'd probably need to expose one blob type property listing the encodings that may work as an array, and another property for setting the one to use. IN_FORMATS property is somewhat similar, although more complicated because it is the combination of format and modifier.
(Since I am using my Gmail Id, I feel I should mention that I work at Nvidia)
Nice to know the source of interest. :-)
Thanks, pq
Thanks, -Yogish
On Thu, May 28, 2020 at 6:18 PM Pekka Paalanen ppaalanen@gmail.com wrote:
On Thu, 28 May 2020 17:38:59 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
I am trying to find a way through Weston which will allow setting
specific
encoding at display output.
Hi,
why do *you* want to control that?
Why not let the driver always choose the highest possible encoding given the video mode and hardware capability?
I can understand userspace wanting to know what it got, but why should userspace be able to control it?
Would people want to pick the encoding first, and then go for the highest possible video mode?
Could you please elaborate on why it is best to let DRM driver automatically configure which encoding to choose rather than making it selectable by DRM client ? I am not able to find reference to past discussion about this. I was only able to find a proposed change
https://lists.freedesktop.org/archives/intel-gfx/2017-April/125451.html
but
am not able to find why it got rejected.
Alternatively, is there existing way through which DRM clients can
specify
preference for output encoding ? Or currently it's all up to the DRM
driver
to choose what output encoding to use.
There must be some reason why userspace needs to be able to control it. I'm also asking as a Weston maintainer, since I'm interested in how this affects e.g. color reproduction or HDR support.
One thing that comes to my mind is using atomic TEST_ONLY commits to probe all the possible video modes × encodings for presenting a list to the user to choose from, if you have a display configuration GUI. E.g with some TV use cases, maybe the user wants to avoid sub-sampling, use the native resolution, but limit refresh rate to what's actually possible. Or any other combination of the three.
Thanks, pq
Thanks, -Yogish
On Thu, May 28, 2020 at 1:54 PM Daniel Vetter daniel@ffwll.ch wrote:
On Thu, May 28, 2020 at 12:29:43PM +0530, Yogish Kulkarni wrote:
For creating new source property, is it good to follow "drm_mode_create_hdmi_colorspace_property()" as an example ? It
seems
that
currently there is no standard DRM property which allows DRM client
to
set
a specific output encoding (like YUV420, YUV422 etc). Also, there is
no
standard property for letting client select YUV/RGB color range. I
see
there are two ways to introduce new properties, 1. do something like drm_mode_create_hdmi_colorspace_property 2. create custom property
similar
to "Broadcast RGB". Is there opinion on which is a preferable way
to
expose
encoding and color rage selection property ?
I guess first question is "why?" Thus far we've gone with the opinion
that
automatically configuring output stuff as much as possible is best.
What's
the use-case where the driver can't select this? -Daniel
Inline..
On Mon, Jun 1, 2020 at 2:19 PM Pekka Paalanen ppaalanen@gmail.com wrote:
On Mon, 1 Jun 2020 09:22:27 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
For letting DRM clients to select output encoding: Sink can support certain display timings with high output bit-depths
using
multiple output encodings, e.g. sink can support a particular timing with RGB 10-bit, YCbCr422 10-bit and YCbCr420 10-bit. So DRM client may want
to
select YCbCr422 10-bit over RBG 10-bit output to reduce the link
bandwidth
(and in turn reduce power/voltage). If DRM driver automatically selects output encoding then we are restricting DRM clients from making
appropriate
choice.
Hi,
right, that seems to be another reason.
For selectable output color range: Certain applications (typically graphics) usually rendered in full range while some applications (typically video) have limited range content.
Since
content can change dynamically, DRM driver does not have enough
information
to choose correct quantization. Only DRM client can correctly select
which
quantization to set (to preserve artist's intent).
Now this is an interesting topic for me. As far as I know, there is no window system protocol to tell the display server whether the application provided content is using full or limited range. This means that the display server cannot tell DRM about full vs. limited range either. It also means that when not fullscreen, the display server cannot show the limited range video content correctly, because it would have to be converted to full-range (or vice versa).
Right, but there could be DRM client which doesn't use window system (e.g.
Gstreamer video sink) and wants to select between full/limited color range. I agree that there is no window system protocol yet but maybe Wayland protocol could be added/extended for this purpose once we finalize things that needs to be done in DRM.
But why would an application produce limited range pixels anyway? Is it
common that hardware video decoders are unable to produce full-range pixels?
The primary reason for why content producer masters video/gfx content as limited range is for compatibility with sinks which only support limited range, and not because video decoders are not capable of decoding full-range content. Also, certain cinema-related content (e.g., movies) may be better suited for limited range encoding due to the level of detail that they need to present/hide (see "Why does limited RGB even exist?" section in https://www.benq.com/en-us/knowledge-center/knowledge/full-rgb-vs-limited-rg... ).
I am asking, because I have a request to add limited vs. full range
information to Wayland.
What about video sinks, including monitors? Are there devices that accept limited-range only, full-range only, or switchable?
Yes, there are sinks which support selectable quantization range and there are sinks which don't. If the quantization range is not selectable, then in general, sources should output full-range for IT timings, and output limited for CE timings. At a high-level, IT timings are part of a standard developed by VESA for computer monitor-like displays. CE (Consumer Electronics) timings are a separate standard for timings more applicable to sinks like consumer TVs, etc.
Why not just always use full-range everywhere?
Or if a sink supports only limited-range, have the display chip automatically convert from full-range, so that software doesn't have to convert in software.
I think it is ok to convert from limited range to full range in display HW pipeline. By "automatically" if you mean display HW or DRM driver should look at the content to figure out whether it is limited range content and then program display pipeline to do the conversion, I don't think that is a good idea since we would need to inspect each pixel. Also, there may be some post-processing done to full-range content that happens to cause the pixel component values to fall within the limited quantization range. How about adding a new DRM KMS plane property to let client convey the driver about input content range? More details on this below.
If you actually have a DRM KMS property for the range, does it mean that:
- the sink is configured to accept that range, and the pixels in the framebuffer need to comply, or
- the display chip converts to that range while framebuffer remains in full-range?
I would imagine this as: (1) Add new read DRM KMS connector property which DRM client will read to know whether sink support selectable quantization range. (2) Add new read/write DRM KMS connector property which DRM client will write to set output quantization range and read to know the current output quantization range. (3) Add new read/write DRM KMS plane property which DRM client will write to set input quantization range and read to know the current input quantization range.
Now lets say if client has limited range content that it wants to display using limited range, it will perform below steps: (A) Set plane's input range property to LIMITED. (B) Set connector's output range property to LIMITED. (C) Read connector property to know whether sink support selectable quantization range: (i) If no, validate HW timing + output range (LIMITED) using atomic test commit, if validation doesn't pass, client should choose another HW timing and revalidate. (ii) if yes, it is not necessary to validate HW timing + output range.
Now lets say if client has limited range content that it wants to display using full range, it will perform below steps: (A) Set plane's input range property to LIMITED (B) Set connector's output range property to FULL (C) Read connector property to know whether sink support selectable quantization range: (i) if no, validate HW timing + output range (FULL) using atomic test commit, if validation doesn't pass, client should choose another HW timing and revalidate (ii) if yes, it is not necessary to validate HW timing + output range. In this example DRM driver will automatically set up display pipeline to do limited to full-range conversion.
Out of the three new properties mentioned above there is another choice for property (1): Instead of expecting client to read whether sink support selectable quantization range and perform validations as mentioned above when quantization range is not selectable, how about adding new flags to drmModeModeInfo->flags and let DRM driver to inform client using this flag whether given HW timing is supported with full range, limited range or both? This will avoid validation step mentioned in (C)(i).
Let me know what you think about the overall proposal mentioned above. If there is no strong disagreement about adding new DRM KMS properties for output quantization range (and output encoding), I'll plan to start working on the changes.
Thanks, -Yogish
If we look at I915 driver's "Broadcast RGB" property, it seems to say to me that the framebuffer is always primarily assumed to be in full-range, and the conversion to limited-range happens in the scanout circuitry. So that property would not help with video content that is already in limited-range.
To recap, there are two orthogonal things: application content or framebuffer range, and video sink / monitor range. The display server between the two, at last if it is a Wayland compositor, would be able to convert as necessary.
For how to use selectable output encoding with Weston: I was thinking that DRM should have separate property to list the
encodings
supported by sink and Weston will present this list to its client. Your
Not client. A configuration tool perhaps, but not generically to all Wayland clients, not as a directly settable knob at least.
idea to validate encodings using TEST_ONLY commit and present a list of timings along with encodings supported by particular timing seems better. Instead of validating all possible encodings, does it make sense to validate only those supported by sink? Irrespective of this we would
Yes, having a list of what the sink actually supports would be nice.
As for Wayland clients, there is an extension brewing at https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/8 that would allow suggesting the optimal encoding (pixel format and modifier really) in flight.
That said, we are talking about the two different things here: framebuffer format vs. encoding on the wire. Whether making them match has benefits is another matter.
anyway need some mechanism which will allow user to select particular encoding for a particular mode. I was thinking to allow this using new
DRM
property "Encoding". Do you have anything better in mind?
I think that is a reasonable and useful goal and idea. Just remember to document it when proposing, even if it seems obvious. The details on how to formulate that into UAPI is up for debate.
As said, changing KMS properties after they have been exposed to userspace won't really work from either kernel or userspace point of view. So you'd probably need to expose one blob type property listing the encodings that may work as an array, and another property for setting the one to use. IN_FORMATS property is somewhat similar, although more complicated because it is the combination of format and modifier.
(Since I am using my Gmail Id, I feel I should mention that I work at Nvidia)
Nice to know the source of interest. :-)
Thanks, pq
Thanks, -Yogish
On Thu, May 28, 2020 at 6:18 PM Pekka Paalanen ppaalanen@gmail.com
wrote:
On Thu, 28 May 2020 17:38:59 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
I am trying to find a way through Weston which will allow setting
specific
encoding at display output.
Hi,
why do *you* want to control that?
Why not let the driver always choose the highest possible encoding given the video mode and hardware capability?
I can understand userspace wanting to know what it got, but why should userspace be able to control it?
Would people want to pick the encoding first, and then go for the highest possible video mode?
Could you please elaborate on why it is best to let DRM driver automatically configure which encoding to choose
rather
than making it selectable by DRM client ? I am not able to find
reference
to past discussion about this. I was only able to find a proposed
change
https://lists.freedesktop.org/archives/intel-gfx/2017-April/125451.html
but
am not able to find why it got rejected.
Alternatively, is there existing way through which DRM clients can
specify
preference for output encoding ? Or currently it's all up to the
DRM
driver
to choose what output encoding to use.
There must be some reason why userspace needs to be able to control it. I'm also asking as a Weston maintainer, since I'm interested in how this affects e.g. color reproduction or HDR support.
One thing that comes to my mind is using atomic TEST_ONLY commits to probe all the possible video modes × encodings for presenting a list to the user to choose from, if you have a display configuration GUI. E.g with some TV use cases, maybe the user wants to avoid sub-sampling, use the native resolution, but limit refresh rate to what's actually possible. Or any other combination of the three.
Thanks, pq
Thanks, -Yogish
On Thu, May 28, 2020 at 1:54 PM Daniel Vetter daniel@ffwll.ch
wrote:
On Thu, May 28, 2020 at 12:29:43PM +0530, Yogish Kulkarni wrote:
For creating new source property, is it good to follow "drm_mode_create_hdmi_colorspace_property()" as an example ?
It
seems
that
currently there is no standard DRM property which allows DRM
client
to
set
a specific output encoding (like YUV420, YUV422 etc). Also,
there is
no
standard property for letting client select YUV/RGB color range.
I
see
there are two ways to introduce new properties, 1. do something
like
drm_mode_create_hdmi_colorspace_property 2. create custom
property
similar
to "Broadcast RGB". Is there opinion on which is a preferable
way
to
expose
encoding and color rage selection property ?
I guess first question is "why?" Thus far we've gone with the
opinion
that
automatically configuring output stuff as much as possible is
best.
What's
the use-case where the driver can't select this? -Daniel
On Wed, 3 Jun 2020 10:50:28 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Inline..
On Mon, Jun 1, 2020 at 2:19 PM Pekka Paalanen ppaalanen@gmail.com wrote:
On Mon, 1 Jun 2020 09:22:27 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
For letting DRM clients to select output encoding: Sink can support certain display timings with high output bit-depths
using
multiple output encodings, e.g. sink can support a particular timing with RGB 10-bit, YCbCr422 10-bit and YCbCr420 10-bit. So DRM client may want
to
select YCbCr422 10-bit over RBG 10-bit output to reduce the link
bandwidth
(and in turn reduce power/voltage). If DRM driver automatically selects output encoding then we are restricting DRM clients from making
appropriate
choice.
Hi,
right, that seems to be another reason.
For selectable output color range: Certain applications (typically graphics) usually rendered in full range while some applications (typically video) have limited range content.
Since
content can change dynamically, DRM driver does not have enough
information
to choose correct quantization. Only DRM client can correctly select
which
quantization to set (to preserve artist's intent).
Now this is an interesting topic for me. As far as I know, there is no window system protocol to tell the display server whether the application provided content is using full or limited range. This means that the display server cannot tell DRM about full vs. limited range either. It also means that when not fullscreen, the display server cannot show the limited range video content correctly, because it would have to be converted to full-range (or vice versa).
Right, but there could be DRM client which doesn't use window system (e.g. Gstreamer video sink) and wants to select between full/limited color range. I agree that there is no window system protocol yet but maybe Wayland protocol could be added/extended for this purpose once we finalize things that needs to be done in DRM.
Hi,
right. If you have that use case and a userspace project welcomes such feature, you're good.
If you propose a KMS property for this, I would hope the patches document or have links pointing to answers to all my questions here. That would help both driver and userspace implementations to get into the same mindset.
But why would an application produce limited range pixels anyway? Is it common that hardware video decoders are unable to produce full-range pixels?
The primary reason for why content producer masters video/gfx content as limited range is for compatibility with sinks which only support limited range, and not because video decoders are not capable of decoding full-range content.
What I was asking is, even if the video content is limited range, why would one not decode it into full-range pixels always and if the sink need limited range, then convert again in hardware? When done right, it makes no difference in output compared to using limited range through-out if both content and sink use limited range.
Also, certain cinema-related content (e.g., movies) may be better suited for limited range encoding due to the level of detail that they need to present/hide (see "Why does limited RGB even exist?" section in https://www.benq.com/en-us/knowledge-center/knowledge/full-rgb-vs-limited-rg... ).
That is a very nice link, thanks!
But to me it seems the section "Why is this a problem?" gets "crushed blacks" backwards, so maybe I just don't get it.
I would assume that if the source (computer) sends full-range pixel values on the wire and the sink (monitor) works in limited-range mode, then you would get crushed blacks and crushed whites.
But if the source sends limited-range data and the sink works in full-range more, you'd get the "washed out" image.
My thinking comes from the mapping of channel values: if 0-16 and 235-255 ranges show no difference within them, I'd call that "crushed". Similarly if one assumes 16 is darkest black and it's actually not, you'd get "washed out" (I might call it compressed instead, because it affects both black and white ends, unable to achieve both the darkest black and the brightest white).
Anyway, I believe I do understand that if you have content in one range and the sink assumes a different range, the content will show poorly. I don't doubt that.
My question instead is: why would it be bad to always convert everything to full-range inside the source (e.g. decoder -> app -> display server all in full-range), and then convert for the wire into what the sink expects?
Because that is how Wayland color management is going to handle differing color spaces, more or less. (Actually, quite likely the compositor internal per-output color space will be the sink's color space but in linear encoding (e.g. fp16 data type) for proper blending.)
I am asking, because I have a request to add limited vs. full range information to Wayland.
What about video sinks, including monitors? Are there devices that accept limited-range only, full-range only, or switchable?
Yes, there are sinks which support selectable quantization range and there are sinks which don't. If the quantization range is not selectable, then in general, sources should output full-range for IT timings, and output limited for CE timings. At a high-level, IT timings are part of a standard developed by VESA for computer monitor-like displays. CE (Consumer Electronics) timings are a separate standard for timings more applicable to sinks like consumer TVs, etc.
Very good. How is this achieved with KMS today? Does the kernel driver automatically make the display chip convert to full-range or limited-range based on the mode information?
Or is this something that simply doesn't exist yet, and it needs userspace to make the decision on which range to program the display hardware to emit into the wire? Hence the need for a range property.
Why not just always use full-range everywhere?
Or if a sink supports only limited-range, have the display chip automatically convert from full-range, so that software doesn't have to convert in software.
I think it is ok to convert from limited range to full range in display HW pipeline.
But that is a conversion that would practically never be used at that point in the pipeline. If a display server works internally (composites) in limited range, it means it will always lose detail from full-range applications, regardless of whether the monitor is full- or limited-range. The display server must always work in full-range (or monitor's range) to avoid that. If the sink/monitor accepts only limited-range, then convert full-range to limited-range as the very last step.
If the sink accepts only limited-range, then necessarily it cannot present full-range content accurately and loss of detail is unavoidable, so the lossy conversion at scanout is ok.
By "automatically" if you mean display HW or DRM driver should look at the content to figure out whether it is limited range content and then program display pipeline to do the conversion, I don't think that is a good idea since we would need to inspect each pixel. Also, there may be some post-processing done to full-range content that happens to cause the pixel component values to fall within the limited quantization range. How about adding a new DRM KMS plane property to let client convey the driver about input content range? More details on this below.
Sorry, a bad choice of word.
I mean "automatically" in the sense that the display server (or KMS app) inspects the sink properties and sets up the display scanout pipeline to convert to the right range. Then the display server does not need to care about compositing in limited-range or to tell apps to produce content in limited-range.
If you actually have a DRM KMS property for the range, does it mean that:
- the sink is configured to accept that range, and the pixels in the framebuffer need to comply, or
- the display chip converts to that range while framebuffer remains in full-range?
I would imagine this as: (1) Add new read DRM KMS connector property which DRM client will read to know whether sink support selectable quantization range.
Good.
(2) Add new read/write DRM KMS connector property which DRM client will write to set output quantization range and read to know the current output quantization range.
Yes, programming the sink's expectation is good.
Btw. just in case, try not to create KMS properties that are both writable by userspace and arbitrarily writable by the kernel as well. It often leads to awkward or racy usage patterns. If the read and write values are completely disconnected, it also might make blind KMS state save/restore impossible. Blind KMS state save/restore is necessary for KMS apps and display servers to ensure they continue running with the same KMS state they had before, e.g. after VT-switching or reboot, even if there are writable properties they do not recognise.
If it's just reading back what userspace last wrote, it's good.
(3) Add new read/write DRM KMS plane property which DRM client will write to set input quantization range and read to know the current input quantization range.
Ok, so these two properties together would define what automatic conversion the display chip does to framebuffer content during scanout.
But there are already other ways too, DEGAMMA/GAMMA LUTs or CTM could be used for it already. Is there a benefit from adding more ways to achieve the same?
You'd have to define how all these properties interact, regardless of whether any driver actually exposes them all at the same time. Plus the existing "Broadcast RGB" property. Or, you have to document what combinations of properties are forbidden for drivers to expose, so that userspace has the correct expectations and know how to use them right.
Now lets say if client has limited range content that it wants to display using limited range, it will perform below steps: (A) Set plane's input range property to LIMITED. (B) Set connector's output range property to LIMITED. (C) Read connector property to know whether sink support selectable quantization range: (i) If no, validate HW timing + output range (LIMITED) using atomic test commit, if validation doesn't pass, client should choose another HW timing and revalidate.
Is the assumption here that the timing implies range, like you explained with IT vs. CE? IOW, the kernel can tell the difference between IT and CE timings just from the timing parameters themselves?
(ii) if yes, it is not necessary to validate HW timing + outputrange.
Given the nature of the atomic KMS UAPI, I'd say it is always necessary to validate. Just because a setting is possible does not imply the combination of all property values you picked is valid.
Now lets say if client has limited range content that it wants to display using full range, it will perform below steps: (A) Set plane's input range property to LIMITED (B) Set connector's output range property to FULL (C) Read connector property to know whether sink support selectable quantization range: (i) if no, validate HW timing + output range (FULL) using atomic test commit, if validation doesn't pass, client should choose another HW timing and revalidate (ii) if yes, it is not necessary to validate HW timing + output range. In this example DRM driver will automatically set up display pipeline to do limited to full-range conversion.
Right.
Out of the three new properties mentioned above there is another choice for property (1): Instead of expecting client to read whether sink support selectable quantization range and perform validations as mentioned above when quantization range is not selectable, how about adding new flags to drmModeModeInfo->flags and let DRM driver to inform client using this flag whether given HW timing is supported with full range, limited range or both? This will avoid validation step mentioned in (C)(i).
I can't tell if that is a good idea or not, but I don't think the validation can be avoided in any case. With atomic, userspace should always validate before assuming.
Let me know what you think about the overall proposal mentioned above. If there is no strong disagreement about adding new DRM KMS properties for output quantization range (and output encoding), I'll plan to start working on the changes.
From my opinion as a Weston maintainer, I think having quantization range and wire encoding would be good to have. The devil is in the details though, as always.
Thanks, pq
Thanks, -Yogish
If we look at I915 driver's "Broadcast RGB" property, it seems to say to me that the framebuffer is always primarily assumed to be in full-range, and the conversion to limited-range happens in the scanout circuitry. So that property would not help with video content that is already in limited-range.
To recap, there are two orthogonal things: application content or framebuffer range, and video sink / monitor range. The display server between the two, at last if it is a Wayland compositor, would be able to convert as necessary.
For how to use selectable output encoding with Weston: I was thinking that DRM should have separate property to list the
encodings
supported by sink and Weston will present this list to its client. Your
Not client. A configuration tool perhaps, but not generically to all Wayland clients, not as a directly settable knob at least.
idea to validate encodings using TEST_ONLY commit and present a list of timings along with encodings supported by particular timing seems better. Instead of validating all possible encodings, does it make sense to validate only those supported by sink? Irrespective of this we would
Yes, having a list of what the sink actually supports would be nice.
As for Wayland clients, there is an extension brewing at https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/8 that would allow suggesting the optimal encoding (pixel format and modifier really) in flight.
That said, we are talking about the two different things here: framebuffer format vs. encoding on the wire. Whether making them match has benefits is another matter.
anyway need some mechanism which will allow user to select particular encoding for a particular mode. I was thinking to allow this using new
DRM
property "Encoding". Do you have anything better in mind?
I think that is a reasonable and useful goal and idea. Just remember to document it when proposing, even if it seems obvious. The details on how to formulate that into UAPI is up for debate.
As said, changing KMS properties after they have been exposed to userspace won't really work from either kernel or userspace point of view. So you'd probably need to expose one blob type property listing the encodings that may work as an array, and another property for setting the one to use. IN_FORMATS property is somewhat similar, although more complicated because it is the combination of format and modifier.
(Since I am using my Gmail Id, I feel I should mention that I work at Nvidia)
Nice to know the source of interest. :-)
Thanks, pq
Thanks, -Yogish
On Thu, May 28, 2020 at 6:18 PM Pekka Paalanen ppaalanen@gmail.com
wrote:
On Thu, 28 May 2020 17:38:59 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
I am trying to find a way through Weston which will allow setting
specific
encoding at display output.
Hi,
why do *you* want to control that?
Why not let the driver always choose the highest possible encoding given the video mode and hardware capability?
I can understand userspace wanting to know what it got, but why should userspace be able to control it?
Would people want to pick the encoding first, and then go for the highest possible video mode?
Could you please elaborate on why it is best to let DRM driver automatically configure which encoding to choose
rather
than making it selectable by DRM client ? I am not able to find
reference
to past discussion about this. I was only able to find a proposed
change
https://lists.freedesktop.org/archives/intel-gfx/2017-April/125451.html
but
am not able to find why it got rejected.
Alternatively, is there existing way through which DRM clients can
specify
preference for output encoding ? Or currently it's all up to the
DRM
driver
to choose what output encoding to use.
There must be some reason why userspace needs to be able to control it. I'm also asking as a Weston maintainer, since I'm interested in how this affects e.g. color reproduction or HDR support.
One thing that comes to my mind is using atomic TEST_ONLY commits to probe all the possible video modes × encodings for presenting a list to the user to choose from, if you have a display configuration GUI. E.g with some TV use cases, maybe the user wants to avoid sub-sampling, use the native resolution, but limit refresh rate to what's actually possible. Or any other combination of the three.
Thanks, pq
Thanks, -Yogish
On Thu, May 28, 2020 at 1:54 PM Daniel Vetter daniel@ffwll.ch
wrote:
On Thu, May 28, 2020 at 12:29:43PM +0530, Yogish Kulkarni wrote: > For creating new source property, is it good to follow > "drm_mode_create_hdmi_colorspace_property()" as an example ?
It
seems
that > currently there is no standard DRM property which allows DRM
client
to
set > a specific output encoding (like YUV420, YUV422 etc). Also,
there is
no
> standard property for letting client select YUV/RGB color range.
I
see
> there are two ways to introduce new properties, 1. do something
like
> drm_mode_create_hdmi_colorspace_property 2. create custom
property
similar > to "Broadcast RGB". Is there opinion on which is a preferable
way
to
expose > encoding and color rage selection property ?
I guess first question is "why?" Thus far we've gone with the
opinion
that
automatically configuring output stuff as much as possible is
best.
What's
the use-case where the driver can't select this? -Daniel
On Wed, Jun 03, 2020 at 12:12:23PM +0300, Pekka Paalanen wrote:
On Wed, 3 Jun 2020 10:50:28 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Inline..
On Mon, Jun 1, 2020 at 2:19 PM Pekka Paalanen ppaalanen@gmail.com wrote:
On Mon, 1 Jun 2020 09:22:27 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
For letting DRM clients to select output encoding: Sink can support certain display timings with high output bit-depths
using
multiple output encodings, e.g. sink can support a particular timing with RGB 10-bit, YCbCr422 10-bit and YCbCr420 10-bit. So DRM client may want
to
select YCbCr422 10-bit over RBG 10-bit output to reduce the link
bandwidth
(and in turn reduce power/voltage). If DRM driver automatically selects output encoding then we are restricting DRM clients from making
appropriate
choice.
Hi,
right, that seems to be another reason.
For selectable output color range: Certain applications (typically graphics) usually rendered in full range while some applications (typically video) have limited range content.
Since
content can change dynamically, DRM driver does not have enough
information
to choose correct quantization. Only DRM client can correctly select
which
quantization to set (to preserve artist's intent).
Now this is an interesting topic for me. As far as I know, there is no window system protocol to tell the display server whether the application provided content is using full or limited range. This means that the display server cannot tell DRM about full vs. limited range either. It also means that when not fullscreen, the display server cannot show the limited range video content correctly, because it would have to be converted to full-range (or vice versa).
Right, but there could be DRM client which doesn't use window system (e.g. Gstreamer video sink) and wants to select between full/limited color range. I agree that there is no window system protocol yet but maybe Wayland protocol could be added/extended for this purpose once we finalize things that needs to be done in DRM.
Hi,
right. If you have that use case and a userspace project welcomes such feature, you're good.
If you propose a KMS property for this, I would hope the patches document or have links pointing to answers to all my questions here. That would help both driver and userspace implementations to get into the same mindset.
But why would an application produce limited range pixels anyway? Is it common that hardware video decoders are unable to produce full-range pixels?
The primary reason for why content producer masters video/gfx content as limited range is for compatibility with sinks which only support limited range, and not because video decoders are not capable of decoding full-range content.
What I was asking is, even if the video content is limited range, why would one not decode it into full-range pixels always and if the sink need limited range, then convert again in hardware? When done right, it makes no difference in output compared to using limited range through-out if both content and sink use limited range.
Also, certain cinema-related content (e.g., movies) may be better suited for limited range encoding due to the level of detail that they need to present/hide (see "Why does limited RGB even exist?" section in https://www.benq.com/en-us/knowledge-center/knowledge/full-rgb-vs-limited-rg... ).
That is a very nice link, thanks!
But to me it seems the section "Why is this a problem?" gets "crushed blacks" backwards, so maybe I just don't get it.
I would assume that if the source (computer) sends full-range pixel values on the wire and the sink (monitor) works in limited-range mode, then you would get crushed blacks and crushed whites.
But if the source sends limited-range data and the sink works in full-range more, you'd get the "washed out" image.
My thinking comes from the mapping of channel values: if 0-16 and 235-255 ranges show no difference within them, I'd call that "crushed". Similarly if one assumes 16 is darkest black and it's actually not, you'd get "washed out" (I might call it compressed instead, because it affects both black and white ends, unable to achieve both the darkest black and the brightest white).
Anyway, I believe I do understand that if you have content in one range and the sink assumes a different range, the content will show poorly. I don't doubt that.
My question instead is: why would it be bad to always convert everything to full-range inside the source (e.g. decoder -> app -> display server all in full-range), and then convert for the wire into what the sink expects?
Because that is how Wayland color management is going to handle differing color spaces, more or less. (Actually, quite likely the compositor internal per-output color space will be the sink's color space but in linear encoding (e.g. fp16 data type) for proper blending.)
I am asking, because I have a request to add limited vs. full range information to Wayland.
What about video sinks, including monitors? Are there devices that accept limited-range only, full-range only, or switchable?
Yes, there are sinks which support selectable quantization range and there are sinks which don't. If the quantization range is not selectable, then in general, sources should output full-range for IT timings, and output limited for CE timings. At a high-level, IT timings are part of a standard developed by VESA for computer monitor-like displays. CE (Consumer Electronics) timings are a separate standard for timings more applicable to sinks like consumer TVs, etc.
Very good. How is this achieved with KMS today? Does the kernel driver automatically make the display chip convert to full-range or limited-range based on the mode information?
Or is this something that simply doesn't exist yet, and it needs userspace to make the decision on which range to program the display hardware to emit into the wire? Hence the need for a range property.
At least i915 handles it all automagically. Older hw generations are nicer and have a simple bit to tell the hardware to do the full->limited range compression, or modern hw we use the csc matrix to achieve the same result. The latter does cause some headaches when this gets combined with user provided gamma/degamma/ctm, and I think we still get some of the more esoteric combinations wrong.
A few years back there was a proposal to extend the 'Broadcast RGB' range prop with a new knob to allow passthrough limited range content (ie. no range compression done during scanout, but sink gets told the content is limited range), but it fell through the cracks.
Hi all,
On Wed, 3 Jun 2020 at 10:57, Ville Syrjälä ville.syrjala@linux.intel.com wrote:
On Wed, Jun 03, 2020 at 12:12:23PM +0300, Pekka Paalanen wrote:
On Wed, 3 Jun 2020 10:50:28 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Inline..
On Mon, Jun 1, 2020 at 2:19 PM Pekka Paalanen ppaalanen@gmail.com wrote:
On Mon, 1 Jun 2020 09:22:27 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
For letting DRM clients to select output encoding: Sink can support certain display timings with high output bit-depths
using
multiple output encodings, e.g. sink can support a particular timing with RGB 10-bit, YCbCr422 10-bit and YCbCr420 10-bit. So DRM client may want
to
select YCbCr422 10-bit over RBG 10-bit output to reduce the link
bandwidth
(and in turn reduce power/voltage). If DRM driver automatically selects output encoding then we are restricting DRM clients from making
appropriate
choice.
Hi,
right, that seems to be another reason.
For selectable output color range: Certain applications (typically graphics) usually rendered in full range while some applications (typically video) have limited range content.
Since
content can change dynamically, DRM driver does not have enough
information
to choose correct quantization. Only DRM client can correctly select
which
quantization to set (to preserve artist's intent).
Now this is an interesting topic for me. As far as I know, there is no window system protocol to tell the display server whether the application provided content is using full or limited range. This means that the display server cannot tell DRM about full vs. limited range either. It also means that when not fullscreen, the display server cannot show the limited range video content correctly, because it would have to be converted to full-range (or vice versa).
Right, but there could be DRM client which doesn't use window system (e.g. Gstreamer video sink) and wants to select between full/limited color range. I agree that there is no window system protocol yet but maybe Wayland protocol could be added/extended for this purpose once we finalize things that needs to be done in DRM.
Hi,
right. If you have that use case and a userspace project welcomes such feature, you're good.
If you propose a KMS property for this, I would hope the patches document or have links pointing to answers to all my questions here. That would help both driver and userspace implementations to get into the same mindset.
But why would an application produce limited range pixels anyway? Is it common that hardware video decoders are unable to produce full-range pixels?
The primary reason for why content producer masters video/gfx content as limited range is for compatibility with sinks which only support limited range, and not because video decoders are not capable of decoding full-range content.
What I was asking is, even if the video content is limited range, why would one not decode it into full-range pixels always and if the sink need limited range, then convert again in hardware? When done right, it makes no difference in output compared to using limited range through-out if both content and sink use limited range.
Also, certain cinema-related content (e.g., movies) may be better suited for limited range encoding due to the level of detail that they need to present/hide (see "Why does limited RGB even exist?" section in https://www.benq.com/en-us/knowledge-center/knowledge/full-rgb-vs-limited-rg... ).
That is a very nice link, thanks!
But to me it seems the section "Why is this a problem?" gets "crushed blacks" backwards, so maybe I just don't get it.
I would assume that if the source (computer) sends full-range pixel values on the wire and the sink (monitor) works in limited-range mode, then you would get crushed blacks and crushed whites.
But if the source sends limited-range data and the sink works in full-range more, you'd get the "washed out" image.
My thinking comes from the mapping of channel values: if 0-16 and 235-255 ranges show no difference within them, I'd call that "crushed". Similarly if one assumes 16 is darkest black and it's actually not, you'd get "washed out" (I might call it compressed instead, because it affects both black and white ends, unable to achieve both the darkest black and the brightest white).
Anyway, I believe I do understand that if you have content in one range and the sink assumes a different range, the content will show poorly. I don't doubt that.
My question instead is: why would it be bad to always convert everything to full-range inside the source (e.g. decoder -> app -> display server all in full-range), and then convert for the wire into what the sink expects?
Because that is how Wayland color management is going to handle differing color spaces, more or less. (Actually, quite likely the compositor internal per-output color space will be the sink's color space but in linear encoding (e.g. fp16 data type) for proper blending.)
I am asking, because I have a request to add limited vs. full range information to Wayland.
What about video sinks, including monitors? Are there devices that accept limited-range only, full-range only, or switchable?
Yes, there are sinks which support selectable quantization range and there are sinks which don't. If the quantization range is not selectable, then in general, sources should output full-range for IT timings, and output limited for CE timings. At a high-level, IT timings are part of a standard developed by VESA for computer monitor-like displays. CE (Consumer Electronics) timings are a separate standard for timings more applicable to sinks like consumer TVs, etc.
Very good. How is this achieved with KMS today? Does the kernel driver automatically make the display chip convert to full-range or limited-range based on the mode information?
Or is this something that simply doesn't exist yet, and it needs userspace to make the decision on which range to program the display hardware to emit into the wire? Hence the need for a range property.
At least i915 handles it all automagically. Older hw generations are nicer and have a simple bit to tell the hardware to do the full->limited range compression, or modern hw we use the csc matrix to achieve the same result. The latter does cause some headaches when this gets combined with user provided gamma/degamma/ctm, and I think we still get some of the more esoteric combinations wrong.
A few years back there was a proposal to extend the 'Broadcast RGB' range prop with a new knob to allow passthrough limited range content (ie. no range compression done during scanout, but sink gets told the content is limited range), but it fell through the cracks.
JFYI the "Broadcast RGB" property is exposed by a couple of drivers - gma500 and i915. If people are planning to work on it, it would make sense to have a proper helper in core drm.
Aside: there are a bunch of other properties which could also use some love [1]
Hi,
On 2020-06-03 11:12, Pekka Paalanen wrote:
On Wed, 3 Jun 2020 10:50:28 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Inline..
On Mon, Jun 1, 2020 at 2:19 PM Pekka Paalanen ppaalanen@gmail.com wrote:
On Mon, 1 Jun 2020 09:22:27 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
Hi,
For letting DRM clients to select output encoding: Sink can support certain display timings with high output bit-depths
using
multiple output encodings, e.g. sink can support a particular timing with RGB 10-bit, YCbCr422 10-bit and YCbCr420 10-bit. So DRM client may want
to
select YCbCr422 10-bit over RBG 10-bit output to reduce the link
bandwidth
(and in turn reduce power/voltage). If DRM driver automatically selects output encoding then we are restricting DRM clients from making
appropriate
choice.
Hi,
right, that seems to be another reason.
For selectable output color range: Certain applications (typically graphics) usually rendered in full range while some applications (typically video) have limited range content.
Since
content can change dynamically, DRM driver does not have enough
information
to choose correct quantization. Only DRM client can correctly select
which
quantization to set (to preserve artist's intent).
Now this is an interesting topic for me. As far as I know, there is no window system protocol to tell the display server whether the application provided content is using full or limited range. This means that the display server cannot tell DRM about full vs. limited range either. It also means that when not fullscreen, the display server cannot show the limited range video content correctly, because it would have to be converted to full-range (or vice versa).
Right, but there could be DRM client which doesn't use window system (e.g. Gstreamer video sink) and wants to select between full/limited color range. I agree that there is no window system protocol yet but maybe Wayland protocol could be added/extended for this purpose once we finalize things that needs to be done in DRM.
Hi,
right. If you have that use case and a userspace project welcomes such feature, you're good.
Kodi is a userspace application that is very interested in being able to control or set preferred HDMI output format (rgb444/yuv444/422/420) and quantization range (full/limited).
Main reason is to allow end-users to make overrides when sink EDID don't fully match the TV/AVR features or when drm driver makes a bad automatic choice. Hans Verkuil's conclusion in HDMI RGB Quantization Range Lessons at [1] hold ture, it is total chaos.
Right now, Kodi set the COLOR_ENCODING and COLOR_RANGE plane properties to let kernel know color encoding and color range of a YUV framebuffer.
A single active plane showing a YUV framebuffer with limited range could hint a drm driver that end-user might want to use YUV and limited range output to prevent any banding effect when watching a movie. But in the case of when there is a second overlay plane for OSD or subtitles it may become very hard to guess what configuration works best for end-user.
I have piggybacked on the "content type" connector property in [2] for my personal use to signal my drm driver if YUV (Movie) or RGB (Graphics) output is preferred this far but proper drm properties would really help :-)
[1] https://elinux.org/images/5/53/Elce2017_0-hdmi.pdf [2] https://github.com/xbmc/xbmc/pull/14358
If you propose a KMS property for this, I would hope the patches document or have links pointing to answers to all my questions here. That would help both driver and userspace implementations to get into the same mindset.
But why would an application produce limited range pixels anyway? Is it common that hardware video decoders are unable to produce full-range pixels?
The primary reason for why content producer masters video/gfx content as limited range is for compatibility with sinks which only support limited range, and not because video decoders are not capable of decoding full-range content.
What I was asking is, even if the video content is limited range, why would one not decode it into full-range pixels always and if the sink need limited range, then convert again in hardware? When done right, it makes no difference in output compared to using limited range through-out if both content and sink use limited range.
For the Allwinner/Amlogic/Rockchip arm devices I mainly play with the video decoder does not support range conversion (to my knowledge) and will produce NV12/YU12 framebuffers in the range the video was encoded in.
These devices typically lack a high-performance GPU/3D-accelerator and may have limited CSC capabilities in the display controller. The HDMI block can usually do simple RGB/YUV and full/limited conversions, but using these conversions typically produce banding effects.
Being able to passthrough decoded framebuffers in the entire pipeline from decoder, display controller and hdmi block typically produce best results.
Regards, Jonas
Also, certain cinema-related content (e.g., movies) may be better suited for limited range encoding due to the level of detail that they need to present/hide (see "Why does limited RGB even exist?" section in https://www.benq.com/en-us/knowledge-center/knowledge/full-rgb-vs-limited-rg... ).
That is a very nice link, thanks!
But to me it seems the section "Why is this a problem?" gets "crushed blacks" backwards, so maybe I just don't get it.
I would assume that if the source (computer) sends full-range pixel values on the wire and the sink (monitor) works in limited-range mode, then you would get crushed blacks and crushed whites.
But if the source sends limited-range data and the sink works in full-range more, you'd get the "washed out" image.
My thinking comes from the mapping of channel values: if 0-16 and 235-255 ranges show no difference within them, I'd call that "crushed". Similarly if one assumes 16 is darkest black and it's actually not, you'd get "washed out" (I might call it compressed instead, because it affects both black and white ends, unable to achieve both the darkest black and the brightest white).
Anyway, I believe I do understand that if you have content in one range and the sink assumes a different range, the content will show poorly. I don't doubt that.
My question instead is: why would it be bad to always convert everything to full-range inside the source (e.g. decoder -> app -> display server all in full-range), and then convert for the wire into what the sink expects?
Because that is how Wayland color management is going to handle differing color spaces, more or less. (Actually, quite likely the compositor internal per-output color space will be the sink's color space but in linear encoding (e.g. fp16 data type) for proper blending.)
I am asking, because I have a request to add limited vs. full range information to Wayland.
What about video sinks, including monitors? Are there devices that accept limited-range only, full-range only, or switchable?
Yes, there are sinks which support selectable quantization range and there are sinks which don't. If the quantization range is not selectable, then in general, sources should output full-range for IT timings, and output limited for CE timings. At a high-level, IT timings are part of a standard developed by VESA for computer monitor-like displays. CE (Consumer Electronics) timings are a separate standard for timings more applicable to sinks like consumer TVs, etc.
Very good. How is this achieved with KMS today? Does the kernel driver automatically make the display chip convert to full-range or limited-range based on the mode information?
Or is this something that simply doesn't exist yet, and it needs userspace to make the decision on which range to program the display hardware to emit into the wire? Hence the need for a range property.
Why not just always use full-range everywhere?
Or if a sink supports only limited-range, have the display chip automatically convert from full-range, so that software doesn't have to convert in software.
I think it is ok to convert from limited range to full range in display HW pipeline.
But that is a conversion that would practically never be used at that point in the pipeline. If a display server works internally (composites) in limited range, it means it will always lose detail from full-range applications, regardless of whether the monitor is full- or limited-range. The display server must always work in full-range (or monitor's range) to avoid that. If the sink/monitor accepts only limited-range, then convert full-range to limited-range as the very last step.
If the sink accepts only limited-range, then necessarily it cannot present full-range content accurately and loss of detail is unavoidable, so the lossy conversion at scanout is ok.
By "automatically" if you mean display HW or DRM driver should look at the content to figure out whether it is limited range content and then program display pipeline to do the conversion, I don't think that is a good idea since we would need to inspect each pixel. Also, there may be some post-processing done to full-range content that happens to cause the pixel component values to fall within the limited quantization range. How about adding a new DRM KMS plane property to let client convey the driver about input content range? More details on this below.
Sorry, a bad choice of word.
I mean "automatically" in the sense that the display server (or KMS app) inspects the sink properties and sets up the display scanout pipeline to convert to the right range. Then the display server does not need to care about compositing in limited-range or to tell apps to produce content in limited-range.
If you actually have a DRM KMS property for the range, does it mean that:
- the sink is configured to accept that range, and the pixels in the framebuffer need to comply, or
- the display chip converts to that range while framebuffer remains in full-range?
I would imagine this as: (1) Add new read DRM KMS connector property which DRM client will read to know whether sink support selectable quantization range.
Good.
(2) Add new read/write DRM KMS connector property which DRM client will write to set output quantization range and read to know the current output quantization range.
Yes, programming the sink's expectation is good.
Btw. just in case, try not to create KMS properties that are both writable by userspace and arbitrarily writable by the kernel as well. It often leads to awkward or racy usage patterns. If the read and write values are completely disconnected, it also might make blind KMS state save/restore impossible. Blind KMS state save/restore is necessary for KMS apps and display servers to ensure they continue running with the same KMS state they had before, e.g. after VT-switching or reboot, even if there are writable properties they do not recognise.
If it's just reading back what userspace last wrote, it's good.
(3) Add new read/write DRM KMS plane property which DRM client will write to set input quantization range and read to know the current input quantization range.
Ok, so these two properties together would define what automatic conversion the display chip does to framebuffer content during scanout.
But there are already other ways too, DEGAMMA/GAMMA LUTs or CTM could be used for it already. Is there a benefit from adding more ways to achieve the same?
You'd have to define how all these properties interact, regardless of whether any driver actually exposes them all at the same time. Plus the existing "Broadcast RGB" property. Or, you have to document what combinations of properties are forbidden for drivers to expose, so that userspace has the correct expectations and know how to use them right.
Now lets say if client has limited range content that it wants to display using limited range, it will perform below steps: (A) Set plane's input range property to LIMITED. (B) Set connector's output range property to LIMITED. (C) Read connector property to know whether sink support selectable quantization range: (i) If no, validate HW timing + output range (LIMITED) using atomic test commit, if validation doesn't pass, client should choose another HW timing and revalidate.
Is the assumption here that the timing implies range, like you explained with IT vs. CE? IOW, the kernel can tell the difference between IT and CE timings just from the timing parameters themselves?
(ii) if yes, it is not necessary to validate HW timing + outputrange.
Given the nature of the atomic KMS UAPI, I'd say it is always necessary to validate. Just because a setting is possible does not imply the combination of all property values you picked is valid.
Now lets say if client has limited range content that it wants to display using full range, it will perform below steps: (A) Set plane's input range property to LIMITED (B) Set connector's output range property to FULL (C) Read connector property to know whether sink support selectable quantization range: (i) if no, validate HW timing + output range (FULL) using atomic test commit, if validation doesn't pass, client should choose another HW timing and revalidate (ii) if yes, it is not necessary to validate HW timing + output range. In this example DRM driver will automatically set up display pipeline to do limited to full-range conversion.
Right.
Out of the three new properties mentioned above there is another choice for property (1): Instead of expecting client to read whether sink support selectable quantization range and perform validations as mentioned above when quantization range is not selectable, how about adding new flags to drmModeModeInfo->flags and let DRM driver to inform client using this flag whether given HW timing is supported with full range, limited range or both? This will avoid validation step mentioned in (C)(i).
I can't tell if that is a good idea or not, but I don't think the validation can be avoided in any case. With atomic, userspace should always validate before assuming.
Let me know what you think about the overall proposal mentioned above. If there is no strong disagreement about adding new DRM KMS properties for output quantization range (and output encoding), I'll plan to start working on the changes.
From my opinion as a Weston maintainer, I think having quantization range and wire encoding would be good to have. The devil is in the details though, as always.
Thanks, pq
Thanks, -Yogish
If we look at I915 driver's "Broadcast RGB" property, it seems to say to me that the framebuffer is always primarily assumed to be in full-range, and the conversion to limited-range happens in the scanout circuitry. So that property would not help with video content that is already in limited-range.
To recap, there are two orthogonal things: application content or framebuffer range, and video sink / monitor range. The display server between the two, at last if it is a Wayland compositor, would be able to convert as necessary.
For how to use selectable output encoding with Weston: I was thinking that DRM should have separate property to list the
encodings
supported by sink and Weston will present this list to its client. Your
Not client. A configuration tool perhaps, but not generically to all Wayland clients, not as a directly settable knob at least.
idea to validate encodings using TEST_ONLY commit and present a list of timings along with encodings supported by particular timing seems better. Instead of validating all possible encodings, does it make sense to validate only those supported by sink? Irrespective of this we would
Yes, having a list of what the sink actually supports would be nice.
As for Wayland clients, there is an extension brewing at https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/8 that would allow suggesting the optimal encoding (pixel format and modifier really) in flight.
That said, we are talking about the two different things here: framebuffer format vs. encoding on the wire. Whether making them match has benefits is another matter.
anyway need some mechanism which will allow user to select particular encoding for a particular mode. I was thinking to allow this using new
DRM
property "Encoding". Do you have anything better in mind?
I think that is a reasonable and useful goal and idea. Just remember to document it when proposing, even if it seems obvious. The details on how to formulate that into UAPI is up for debate.
As said, changing KMS properties after they have been exposed to userspace won't really work from either kernel or userspace point of view. So you'd probably need to expose one blob type property listing the encodings that may work as an array, and another property for setting the one to use. IN_FORMATS property is somewhat similar, although more complicated because it is the combination of format and modifier.
(Since I am using my Gmail Id, I feel I should mention that I work at Nvidia)
Nice to know the source of interest. :-)
Thanks, pq
Thanks, -Yogish
On Thu, May 28, 2020 at 6:18 PM Pekka Paalanen ppaalanen@gmail.com
wrote:
On Thu, 28 May 2020 17:38:59 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
I am trying to find a way through Weston which will allow setting
specific
encoding at display output.
Hi,
why do *you* want to control that?
Why not let the driver always choose the highest possible encoding given the video mode and hardware capability?
I can understand userspace wanting to know what it got, but why should userspace be able to control it?
Would people want to pick the encoding first, and then go for the highest possible video mode?
Could you please elaborate on why it is best to let DRM driver automatically configure which encoding to choose
rather
than making it selectable by DRM client ? I am not able to find
reference
to past discussion about this. I was only able to find a proposed
change
https://lists.freedesktop.org/archives/intel-gfx/2017-April/125451.html
but
am not able to find why it got rejected.
Alternatively, is there existing way through which DRM clients can
specify
preference for output encoding ? Or currently it's all up to the
DRM
driver
to choose what output encoding to use.
There must be some reason why userspace needs to be able to control it. I'm also asking as a Weston maintainer, since I'm interested in how this affects e.g. color reproduction or HDR support.
One thing that comes to my mind is using atomic TEST_ONLY commits to probe all the possible video modes × encodings for presenting a list to the user to choose from, if you have a display configuration GUI. E.g with some TV use cases, maybe the user wants to avoid sub-sampling, use the native resolution, but limit refresh rate to what's actually possible. Or any other combination of the three.
Thanks, pq
Thanks, -Yogish
On Thu, May 28, 2020 at 1:54 PM Daniel Vetter daniel@ffwll.ch
wrote:
> On Thu, May 28, 2020 at 12:29:43PM +0530, Yogish Kulkarni wrote: >> For creating new source property, is it good to follow >> "drm_mode_create_hdmi_colorspace_property()" as an example ?
It
seems
> that >> currently there is no standard DRM property which allows DRM
client
to
> set >> a specific output encoding (like YUV420, YUV422 etc). Also,
there is
no
>> standard property for letting client select YUV/RGB color range.
I
see
>> there are two ways to introduce new properties, 1. do something
like
>> drm_mode_create_hdmi_colorspace_property 2. create custom
property
> similar >> to "Broadcast RGB". Is there opinion on which is a preferable
way
to
> expose >> encoding and color rage selection property ? > > I guess first question is "why?" Thus far we've gone with the
opinion
that
> automatically configuring output stuff as much as possible is
best.
What's
> the use-case where the driver can't select this? > -Daniel
dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
On Wed, 03 Jun 2020 20:20:44 +0000 (UTC) Jonas Karlman jonas@kwiboo.se wrote:
Hi,
On 2020-06-03 11:12, Pekka Paalanen wrote:
On Wed, 3 Jun 2020 10:50:28 +0530 Yogish Kulkarni yogishkulkarni@gmail.com wrote:
...
The primary reason for why content producer masters video/gfx content as limited range is for compatibility with sinks which only support limited range, and not because video decoders are not capable of decoding full-range content.
What I was asking is, even if the video content is limited range, why would one not decode it into full-range pixels always and if the sink need limited range, then convert again in hardware? When done right, it makes no difference in output compared to using limited range through-out if both content and sink use limited range.
For the Allwinner/Amlogic/Rockchip arm devices I mainly play with the video decoder does not support range conversion (to my knowledge) and will produce NV12/YU12 framebuffers in the range the video was encoded in.
These devices typically lack a high-performance GPU/3D-accelerator and may have limited CSC capabilities in the display controller. The HDMI block can usually do simple RGB/YUV and full/limited conversions, but using these conversions typically produce banding effects.
Being able to passthrough decoded framebuffers in the entire pipeline from decoder, display controller and hdmi block typically produce best results.
This is very helpful. It means I really do need to take range into account in Wayland protocol and make sure it can be communicated.
Thanks, pq
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