Can someone provide a deeper explanation about exactly what this property represents please?
Does this represent the range of YCbCr values _into_ a YCbCr-to-RGB conversion (in other words, the range of values in the framebuffer), or the expected output range from the conversion?
This matters, because a "limited", (iow, eg, BT601 compliant YCbCr) framebuffer where the Y signal is between 16..235 being displayed on a full-range RGB output would need different conversion from needing a limited-range RGB output.
If it is indeed the output, then why is this a property of the plane? Is that not a property of:
(a) whether the plane is being blended or overlaid onto a graphics plane which uses full-range RGB (b) the properties of the output(s) to which the plane is being displayed.
IOW, it seems that the output of the CSC is more to do with what's downstream of the plane than with the plane itself.
For example, take this situation:
plane 0 - graphics, full range RGB >-- CRTC --> HDMI sink only supporting plane 1 - video, limited range YUV limited range RGB
In order to display the graphics correctly in that scenario, the HDMI output needs to compress the RGB 0-255 range down to 16..236 to be compliant. If the video is limited range, and the CSC produces a limited range RGB output, then plane 1 gets its range further compressed at the HDMI output, which surely is undesirable.
It would surely be better, if it's not possible to map the range of plane 0 to limited range, to instead expand the YUV range and then recompress it at the HDMI output to match the capabilities of the attached source.
It also seems logical that describing the range of the RGB plane would also be sane - if the application is limiting graphics RGB to 16..235, then you'd want the CSC output to do the same and there'd be no need for any range expansion or compression.
I'd personally like drm_plane_create_color_properties() to allow creation of COLOR_ENCODING without COLOR_RANGE (iow, supported_ranges being zero) until COLOR_RANGE is better defined than it is at present.
Thoughts?
I'm bringing this up, because the hardware I have has a CSC that accepts BT601 and BT709 formats, controlled by a single bit. Another bit controls whether the CSC produces 0..255 output or 16..235 output. That is then blended/overlaid with the graphics plane (0..255) and sent to the output. Having a "limited range" YUV plane produce 16..235 range output makes it look low-contrast compared to the graphics, which is what would be expected - "16" is not black compared to the black of the graphics in the same way that "235" is not white compared to the graphics.
On Tue, Jul 03, 2018 at 05:18:57PM +0100, Russell King - ARM Linux wrote:
Can someone provide a deeper explanation about exactly what this property represents please?
Does this represent the range of YCbCr values _into_ a YCbCr-to-RGB conversion (in other words, the range of values in the framebuffer), or the expected output range from the conversion?
This matters, because a "limited", (iow, eg, BT601 compliant YCbCr) framebuffer where the Y signal is between 16..235 being displayed on a full-range RGB output would need different conversion from needing a limited-range RGB output.
If it is indeed the output, then why is this a property of the plane? Is that not a property of:
(a) whether the plane is being blended or overlaid onto a graphics plane which uses full-range RGB (b) the properties of the output(s) to which the plane is being displayed.
IOW, it seems that the output of the CSC is more to do with what's downstream of the plane than with the plane itself.
For example, take this situation:
plane 0 - graphics, full range RGB >-- CRTC --> HDMI sink only supporting plane 1 - video, limited range YUV limited range RGB
In order to display the graphics correctly in that scenario, the HDMI output needs to compress the RGB 0-255 range down to 16..236 to be compliant. If the video is limited range, and the CSC produces a limited range RGB output, then plane 1 gets its range further compressed at the HDMI output, which surely is undesirable.
It would surely be better, if it's not possible to map the range of plane 0 to limited range, to instead expand the YUV range and then recompress it at the HDMI output to match the capabilities of the attached source.
It also seems logical that describing the range of the RGB plane would also be sane - if the application is limiting graphics RGB to 16..235, then you'd want the CSC output to do the same and there'd be no need for any range expansion or compression.
I'd personally like drm_plane_create_color_properties() to allow creation of COLOR_ENCODING without COLOR_RANGE (iow, supported_ranges being zero) until COLOR_RANGE is better defined than it is at present.
Thoughts?
I'm bringing this up, because the hardware I have has a CSC that accepts BT601 and BT709 formats, controlled by a single bit. Another bit controls whether the CSC produces 0..255 output or 16..235 output. That is then blended/overlaid with the graphics plane (0..255) and sent to the output. Having a "limited range" YUV plane produce 16..235 range output makes it look low-contrast compared to the graphics, which is what would be expected - "16" is not black compared to the black of the graphics in the same way that "235" is not white compared to the graphics.
Drivers are supposed to automatically figure this out by looking at the edid. In i915 we also allow userspace to override this with the "Broadcast RGB" property on the connector. Unfortunately we haven't polished that property yet (not sure what other drivers are doing tbh), so it's only listed in the Documentation/gpu/kms-properties.csv graveyard :-/
For the blending in-between right now the expectation is that the kernel driver figures out a blending path that wastes the least amount of precision. Depending upon hw that might mean blending in full RGB and limiting later on, or converting all planes to limited RGB first. Interactons with the CSC on the crtc for color corrections are also not all that well defined. -Daniel
On Wed, Jul 04, 2018 at 10:26:04AM +0200, Daniel Vetter wrote:
On Tue, Jul 03, 2018 at 05:18:57PM +0100, Russell King - ARM Linux wrote:
Can someone provide a deeper explanation about exactly what this property represents please?
Does this represent the range of YCbCr values _into_ a YCbCr-to-RGB conversion (in other words, the range of values in the framebuffer), or the expected output range from the conversion?
This matters, because a "limited", (iow, eg, BT601 compliant YCbCr) framebuffer where the Y signal is between 16..235 being displayed on a full-range RGB output would need different conversion from needing a limited-range RGB output.
If it is indeed the output, then why is this a property of the plane? Is that not a property of:
(a) whether the plane is being blended or overlaid onto a graphics plane which uses full-range RGB (b) the properties of the output(s) to which the plane is being displayed.
IOW, it seems that the output of the CSC is more to do with what's downstream of the plane than with the plane itself.
For example, take this situation:
plane 0 - graphics, full range RGB >-- CRTC --> HDMI sink only supporting plane 1 - video, limited range YUV limited range RGB
In order to display the graphics correctly in that scenario, the HDMI output needs to compress the RGB 0-255 range down to 16..236 to be compliant. If the video is limited range, and the CSC produces a limited range RGB output, then plane 1 gets its range further compressed at the HDMI output, which surely is undesirable.
It would surely be better, if it's not possible to map the range of plane 0 to limited range, to instead expand the YUV range and then recompress it at the HDMI output to match the capabilities of the attached source.
It also seems logical that describing the range of the RGB plane would also be sane - if the application is limiting graphics RGB to 16..235, then you'd want the CSC output to do the same and there'd be no need for any range expansion or compression.
I'd personally like drm_plane_create_color_properties() to allow creation of COLOR_ENCODING without COLOR_RANGE (iow, supported_ranges being zero) until COLOR_RANGE is better defined than it is at present.
Thoughts?
I'm bringing this up, because the hardware I have has a CSC that accepts BT601 and BT709 formats, controlled by a single bit. Another bit controls whether the CSC produces 0..255 output or 16..235 output. That is then blended/overlaid with the graphics plane (0..255) and sent to the output. Having a "limited range" YUV plane produce 16..235 range output makes it look low-contrast compared to the graphics, which is what would be expected - "16" is not black compared to the black of the graphics in the same way that "235" is not white compared to the graphics.
Drivers are supposed to automatically figure this out by looking at the edid. In i915 we also allow userspace to override this with the "Broadcast RGB" property on the connector. Unfortunately we haven't polished that property yet (not sure what other drivers are doing tbh), so it's only listed in the Documentation/gpu/kms-properties.csv graveyard :-/
In which case, I'd like to implement the COLOR_ENCODING property but not the COLOR_RANGE property until COLOR_RANGE is better defined. Unfortunately, at the moment the choices are to have either both properties or no properties - drm_plane_create_color_properties() doesn't support only creating the encoding property.
Implementing it without it being well defined is a recipe for having a broken UAPI. So, I propose:
8<===== From: Russell King rmk+kernel@armlinux.org.uk Subject: drm: allow COLOR_RANGE property to be optional
The COLOR_RANGE plane property is not well defined - it doesn't define where in the colour conversion this control is applied. If it's an attribute of the data in the plane, then it has the reverse effect from if it's an attribute of the range of RGB output from the plane colour converter.
Rather than being forced to implement this control when wanting the COLOR_ENCODING property, make it optional instead. --- drivers/gpu/drm/drm_color_mgmt.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c index b97e2de2c029..fc397fcf80ab 100644 --- a/drivers/gpu/drm/drm_color_mgmt.c +++ b/drivers/gpu/drm/drm_color_mgmt.c @@ -426,9 +426,9 @@ int drm_plane_create_color_properties(struct drm_plane *plane, (supported_encodings & BIT(default_encoding)) == 0)) return -EINVAL;
- if (WARN_ON(supported_ranges == 0 || - (supported_ranges & -BIT(DRM_COLOR_RANGE_MAX)) != 0 || - (supported_ranges & BIT(default_range)) == 0)) + if (WARN_ON(supported_ranges != 0 && + ((supported_ranges & -BIT(DRM_COLOR_RANGE_MAX)) != 0 || + (supported_ranges & BIT(default_range)) == 0))) return -EINVAL;
len = 0; @@ -450,6 +450,9 @@ int drm_plane_create_color_properties(struct drm_plane *plane, if (plane->state) plane->state->color_encoding = default_encoding;
+ if (supported_ranges == 0) + return 0; + len = 0; for (i = 0; i < DRM_COLOR_RANGE_MAX; i++) { if ((supported_ranges & BIT(i)) == 0)
On Wed, Jul 04, 2018 at 10:05:41AM +0100, Russell King - ARM Linux wrote:
On Wed, Jul 04, 2018 at 10:26:04AM +0200, Daniel Vetter wrote:
On Tue, Jul 03, 2018 at 05:18:57PM +0100, Russell King - ARM Linux wrote:
Can someone provide a deeper explanation about exactly what this property represents please?
Does this represent the range of YCbCr values _into_ a YCbCr-to-RGB conversion (in other words, the range of values in the framebuffer), or the expected output range from the conversion?
This matters, because a "limited", (iow, eg, BT601 compliant YCbCr) framebuffer where the Y signal is between 16..235 being displayed on a full-range RGB output would need different conversion from needing a limited-range RGB output.
If it is indeed the output, then why is this a property of the plane? Is that not a property of:
(a) whether the plane is being blended or overlaid onto a graphics plane which uses full-range RGB (b) the properties of the output(s) to which the plane is being displayed.
IOW, it seems that the output of the CSC is more to do with what's downstream of the plane than with the plane itself.
For example, take this situation:
plane 0 - graphics, full range RGB >-- CRTC --> HDMI sink only supporting plane 1 - video, limited range YUV limited range RGB
In order to display the graphics correctly in that scenario, the HDMI output needs to compress the RGB 0-255 range down to 16..236 to be compliant. If the video is limited range, and the CSC produces a limited range RGB output, then plane 1 gets its range further compressed at the HDMI output, which surely is undesirable.
It would surely be better, if it's not possible to map the range of plane 0 to limited range, to instead expand the YUV range and then recompress it at the HDMI output to match the capabilities of the attached source.
It also seems logical that describing the range of the RGB plane would also be sane - if the application is limiting graphics RGB to 16..235, then you'd want the CSC output to do the same and there'd be no need for any range expansion or compression.
I'd personally like drm_plane_create_color_properties() to allow creation of COLOR_ENCODING without COLOR_RANGE (iow, supported_ranges being zero) until COLOR_RANGE is better defined than it is at present.
Thoughts?
I'm bringing this up, because the hardware I have has a CSC that accepts BT601 and BT709 formats, controlled by a single bit. Another bit controls whether the CSC produces 0..255 output or 16..235 output. That is then blended/overlaid with the graphics plane (0..255) and sent to the output. Having a "limited range" YUV plane produce 16..235 range output makes it look low-contrast compared to the graphics, which is what would be expected - "16" is not black compared to the black of the graphics in the same way that "235" is not white compared to the graphics.
Drivers are supposed to automatically figure this out by looking at the edid. In i915 we also allow userspace to override this with the "Broadcast RGB" property on the connector. Unfortunately we haven't polished that property yet (not sure what other drivers are doing tbh), so it's only listed in the Documentation/gpu/kms-properties.csv graveyard :-/
In which case, I'd like to implement the COLOR_ENCODING property but not the COLOR_RANGE property until COLOR_RANGE is better defined. Unfortunately, at the moment the choices are to have either both properties or no properties - drm_plane_create_color_properties() doesn't support only creating the encoding property.
Implementing it without it being well defined is a recipe for having a broken UAPI. So, I propose:
Hm maybe I misunderstood, but I thought the COLOR_RANGE is on the input side. And you need to adjust your CSC to make sure the output range is whatever makes things Just Work. Probably better to poke Ville on these details, and then clarify the docs.
The commit adding the color stuff also doesn't point at the userspace, and I'm too lazy to dig it out, so no idea how it's supposed to work. Ideally we'll end up with a patch to add a nice graph to the docs. -Daniel
8<===== From: Russell King rmk+kernel@armlinux.org.uk Subject: drm: allow COLOR_RANGE property to be optional
The COLOR_RANGE plane property is not well defined - it doesn't define where in the colour conversion this control is applied. If it's an attribute of the data in the plane, then it has the reverse effect from if it's an attribute of the range of RGB output from the plane colour converter.
Rather than being forced to implement this control when wanting the COLOR_ENCODING property, make it optional instead.
drivers/gpu/drm/drm_color_mgmt.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c index b97e2de2c029..fc397fcf80ab 100644 --- a/drivers/gpu/drm/drm_color_mgmt.c +++ b/drivers/gpu/drm/drm_color_mgmt.c @@ -426,9 +426,9 @@ int drm_plane_create_color_properties(struct drm_plane *plane, (supported_encodings & BIT(default_encoding)) == 0)) return -EINVAL;
- if (WARN_ON(supported_ranges == 0 ||
(supported_ranges & -BIT(DRM_COLOR_RANGE_MAX)) != 0 ||(supported_ranges & BIT(default_range)) == 0))
if (WARN_ON(supported_ranges != 0 &&
((supported_ranges & -BIT(DRM_COLOR_RANGE_MAX)) != 0 ||(supported_ranges & BIT(default_range)) == 0)))return -EINVAL;
len = 0;
@@ -450,6 +450,9 @@ int drm_plane_create_color_properties(struct drm_plane *plane, if (plane->state) plane->state->color_encoding = default_encoding;
- if (supported_ranges == 0)
return 0;- len = 0; for (i = 0; i < DRM_COLOR_RANGE_MAX; i++) { if ((supported_ranges & BIT(i)) == 0)
-- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 13.8Mbps down 630kbps up According to speedtest.net: 13Mbps down 490kbps up
On Wed, Jul 04, 2018 at 11:24:10AM +0200, Daniel Vetter wrote:
On Wed, Jul 04, 2018 at 10:05:41AM +0100, Russell King - ARM Linux wrote:
On Wed, Jul 04, 2018 at 10:26:04AM +0200, Daniel Vetter wrote:
On Tue, Jul 03, 2018 at 05:18:57PM +0100, Russell King - ARM Linux wrote:
Can someone provide a deeper explanation about exactly what this property represents please?
Does this represent the range of YCbCr values _into_ a YCbCr-to-RGB conversion (in other words, the range of values in the framebuffer), or the expected output range from the conversion?
This matters, because a "limited", (iow, eg, BT601 compliant YCbCr) framebuffer where the Y signal is between 16..235 being displayed on a full-range RGB output would need different conversion from needing a limited-range RGB output.
If it is indeed the output, then why is this a property of the plane? Is that not a property of:
(a) whether the plane is being blended or overlaid onto a graphics plane which uses full-range RGB (b) the properties of the output(s) to which the plane is being displayed.
IOW, it seems that the output of the CSC is more to do with what's downstream of the plane than with the plane itself.
For example, take this situation:
plane 0 - graphics, full range RGB >-- CRTC --> HDMI sink only supporting plane 1 - video, limited range YUV limited range RGB
In order to display the graphics correctly in that scenario, the HDMI output needs to compress the RGB 0-255 range down to 16..236 to be compliant. If the video is limited range, and the CSC produces a limited range RGB output, then plane 1 gets its range further compressed at the HDMI output, which surely is undesirable.
It would surely be better, if it's not possible to map the range of plane 0 to limited range, to instead expand the YUV range and then recompress it at the HDMI output to match the capabilities of the attached source.
It also seems logical that describing the range of the RGB plane would also be sane - if the application is limiting graphics RGB to 16..235, then you'd want the CSC output to do the same and there'd be no need for any range expansion or compression.
I'd personally like drm_plane_create_color_properties() to allow creation of COLOR_ENCODING without COLOR_RANGE (iow, supported_ranges being zero) until COLOR_RANGE is better defined than it is at present.
Thoughts?
I'm bringing this up, because the hardware I have has a CSC that accepts BT601 and BT709 formats, controlled by a single bit. Another bit controls whether the CSC produces 0..255 output or 16..235 output. That is then blended/overlaid with the graphics plane (0..255) and sent to the output. Having a "limited range" YUV plane produce 16..235 range output makes it look low-contrast compared to the graphics, which is what would be expected - "16" is not black compared to the black of the graphics in the same way that "235" is not white compared to the graphics.
Drivers are supposed to automatically figure this out by looking at the edid. In i915 we also allow userspace to override this with the "Broadcast RGB" property on the connector. Unfortunately we haven't polished that property yet (not sure what other drivers are doing tbh), so it's only listed in the Documentation/gpu/kms-properties.csv graveyard :-/
In which case, I'd like to implement the COLOR_ENCODING property but not the COLOR_RANGE property until COLOR_RANGE is better defined. Unfortunately, at the moment the choices are to have either both properties or no properties - drm_plane_create_color_properties() doesn't support only creating the encoding property.
Implementing it without it being well defined is a recipe for having a broken UAPI. So, I propose:
Hm maybe I misunderstood, but I thought the COLOR_RANGE is on the input side.
If that's the case, I should force it to only indicate support for limited range, while programming the CSC to produce full range RGB on its output (see below).
And you need to adjust your CSC to make sure the output range is whatever makes things Just Work. Probably better to poke Ville on these details, and then clarify the docs.
It's not possible to arbitarily program the CSC - I have two bits:
- one bit selects whether BT601 or BT709 YUV encoding is used on the CSC input. - one bit selects whether limited or full range RGB is produced on the CSC output.
Given that I have to assume that the primary plane contains full range RGB values (DRM has no means to communicate from userspace anything else at present) I have to always select full range RGB at the CSC output to be blended with the primary plane.
I then need some way to know that the TDA998x is being fed by a full range RGB (for the time being, I'm going to assume that's the case) and convert to limited range in the TDA998x if the sink doesn't support full range. I'm proposing to implement your i915 "broadcast rgb" control in TDA998x to allow that to be overridden - maybe that should become a standardised control for HDMI outputs?
As an optimisation, if the primary plane is disabled, then it would be possible (in theory) to have the plane CSC produce limited range and feed that straight to the TDA998x with no conversion there - but it's probably not feasible to switch both modes without some artifacts being generated, especially as we're talking over I2C to the TDA998x. Also, as mentioned above, the TDA998x has no way to know the format from the upstream CRTC, since it can't assume what DRM driver it is being used with, and the DRM driver can't really assume that the down-stream device is a TDA998x. (I have the same problem with the bus format used between the TDA998x and CRTC, and I notice comments in DRM talking about inter-bridge bus formats also being a problem - it's all the same issue really.)
On Wed, Jul 4, 2018 at 11:58 AM, Russell King - ARM Linux linux@armlinux.org.uk wrote:
On Wed, Jul 04, 2018 at 11:24:10AM +0200, Daniel Vetter wrote:
On Wed, Jul 04, 2018 at 10:05:41AM +0100, Russell King - ARM Linux wrote:
On Wed, Jul 04, 2018 at 10:26:04AM +0200, Daniel Vetter wrote:
On Tue, Jul 03, 2018 at 05:18:57PM +0100, Russell King - ARM Linux wrote:
Can someone provide a deeper explanation about exactly what this property represents please?
Does this represent the range of YCbCr values _into_ a YCbCr-to-RGB conversion (in other words, the range of values in the framebuffer), or the expected output range from the conversion?
This matters, because a "limited", (iow, eg, BT601 compliant YCbCr) framebuffer where the Y signal is between 16..235 being displayed on a full-range RGB output would need different conversion from needing a limited-range RGB output.
If it is indeed the output, then why is this a property of the plane? Is that not a property of:
(a) whether the plane is being blended or overlaid onto a graphics plane which uses full-range RGB (b) the properties of the output(s) to which the plane is being displayed.
IOW, it seems that the output of the CSC is more to do with what's downstream of the plane than with the plane itself.
For example, take this situation:
plane 0 - graphics, full range RGB >-- CRTC --> HDMI sink only supporting plane 1 - video, limited range YUV limited range RGB
In order to display the graphics correctly in that scenario, the HDMI output needs to compress the RGB 0-255 range down to 16..236 to be compliant. If the video is limited range, and the CSC produces a limited range RGB output, then plane 1 gets its range further compressed at the HDMI output, which surely is undesirable.
It would surely be better, if it's not possible to map the range of plane 0 to limited range, to instead expand the YUV range and then recompress it at the HDMI output to match the capabilities of the attached source.
It also seems logical that describing the range of the RGB plane would also be sane - if the application is limiting graphics RGB to 16..235, then you'd want the CSC output to do the same and there'd be no need for any range expansion or compression.
I'd personally like drm_plane_create_color_properties() to allow creation of COLOR_ENCODING without COLOR_RANGE (iow, supported_ranges being zero) until COLOR_RANGE is better defined than it is at present.
Thoughts?
I'm bringing this up, because the hardware I have has a CSC that accepts BT601 and BT709 formats, controlled by a single bit. Another bit controls whether the CSC produces 0..255 output or 16..235 output. That is then blended/overlaid with the graphics plane (0..255) and sent to the output. Having a "limited range" YUV plane produce 16..235 range output makes it look low-contrast compared to the graphics, which is what would be expected - "16" is not black compared to the black of the graphics in the same way that "235" is not white compared to the graphics.
Drivers are supposed to automatically figure this out by looking at the edid. In i915 we also allow userspace to override this with the "Broadcast RGB" property on the connector. Unfortunately we haven't polished that property yet (not sure what other drivers are doing tbh), so it's only listed in the Documentation/gpu/kms-properties.csv graveyard :-/
In which case, I'd like to implement the COLOR_ENCODING property but not the COLOR_RANGE property until COLOR_RANGE is better defined. Unfortunately, at the moment the choices are to have either both properties or no properties - drm_plane_create_color_properties() doesn't support only creating the encoding property.
Implementing it without it being well defined is a recipe for having a broken UAPI. So, I propose:
Hm maybe I misunderstood, but I thought the COLOR_RANGE is on the input side.
If that's the case, I should force it to only indicate support for limited range, while programming the CSC to produce full range RGB on its output (see below).
Agreed (as far as my understanding of all this goes at least).
And you need to adjust your CSC to make sure the output range is whatever makes things Just Work. Probably better to poke Ville on these details, and then clarify the docs.
It's not possible to arbitarily program the CSC - I have two bits:
- one bit selects whether BT601 or BT709 YUV encoding is used on the CSC input.
- one bit selects whether limited or full range RGB is produced on the CSC output.
Given that I have to assume that the primary plane contains full range RGB values (DRM has no means to communicate from userspace anything else at present) I have to always select full range RGB at the CSC output to be blended with the primary plane.
You could attach the color range stuff also to the primary plane, but I don't think any current userspace is prepared to use it.
I then need some way to know that the TDA998x is being fed by a full range RGB (for the time being, I'm going to assume that's the case) and convert to limited range in the TDA998x if the sink doesn't support full range. I'm proposing to implement your i915 "broadcast rgb" control in TDA998x to allow that to be overridden - maybe that should become a standardised control for HDMI outputs?
Yup that sounds like a very good idea, plus documenting it in
https://dri.freedesktop.org/docs/drm/gpu/drm-kms.html#hdmi-specific-connecto...
As an optimisation, if the primary plane is disabled, then it would be possible (in theory) to have the plane CSC produce limited range and feed that straight to the TDA998x with no conversion there - but it's probably not feasible to switch both modes without some artifacts being generated, especially as we're talking over I2C to the TDA998x. Also, as mentioned above, the TDA998x has no way to know the format from the upstream CRTC, since it can't assume what DRM driver it is being used with, and the DRM driver can't really assume that the down-stream device is a TDA998x. (I have the same problem with the bus format used between the TDA998x and CRTC, and I notice comments in DRM talking about inter-bridge bus formats also being a problem - it's all the same issue really.)
Yeah atm the entire "what exactly is being feed from the crtc to the bridge" question is rather open and unsolved. Even more so if you have multiple bridges in a chain. There's ideas floating around to add a drm_bridge_state (we have support for adding arbitrary internal state structures now), but nothing came of those efforts yet. For now just hacking around with baked-in assumptions like "tda998x always gets full range on its input side" seems to be good enough still.
There's some high inertia to fix this since you need to get all m bridge drivers and all n drm drivers to align on something, or otherwise it won't really work. And yes the bus format is the exact same issue. There's also been issues around mode polarity and exact timings (if you e.g. have a buffer in your bridge capable of limited timing transformations). -Daniel
On Wed, Jul 04, 2018 at 01:06:42PM +0200, Daniel Vetter wrote:
On Wed, Jul 4, 2018 at 11:58 AM, Russell King - ARM Linux linux@armlinux.org.uk wrote:
On Wed, Jul 04, 2018 at 11:24:10AM +0200, Daniel Vetter wrote:
On Wed, Jul 04, 2018 at 10:05:41AM +0100, Russell King - ARM Linux wrote:
On Wed, Jul 04, 2018 at 10:26:04AM +0200, Daniel Vetter wrote:
On Tue, Jul 03, 2018 at 05:18:57PM +0100, Russell King - ARM Linux wrote:
Can someone provide a deeper explanation about exactly what this property represents please?
Does this represent the range of YCbCr values _into_ a YCbCr-to-RGB conversion (in other words, the range of values in the framebuffer), or the expected output range from the conversion?
This matters, because a "limited", (iow, eg, BT601 compliant YCbCr) framebuffer where the Y signal is between 16..235 being displayed on a full-range RGB output would need different conversion from needing a limited-range RGB output.
If it is indeed the output, then why is this a property of the plane? Is that not a property of:
(a) whether the plane is being blended or overlaid onto a graphics plane which uses full-range RGB (b) the properties of the output(s) to which the plane is being displayed.
IOW, it seems that the output of the CSC is more to do with what's downstream of the plane than with the plane itself.
For example, take this situation:
plane 0 - graphics, full range RGB >-- CRTC --> HDMI sink only supporting plane 1 - video, limited range YUV limited range RGB
In order to display the graphics correctly in that scenario, the HDMI output needs to compress the RGB 0-255 range down to 16..236 to be compliant. If the video is limited range, and the CSC produces a limited range RGB output, then plane 1 gets its range further compressed at the HDMI output, which surely is undesirable.
It would surely be better, if it's not possible to map the range of plane 0 to limited range, to instead expand the YUV range and then recompress it at the HDMI output to match the capabilities of the attached source.
It also seems logical that describing the range of the RGB plane would also be sane - if the application is limiting graphics RGB to 16..235, then you'd want the CSC output to do the same and there'd be no need for any range expansion or compression.
I'd personally like drm_plane_create_color_properties() to allow creation of COLOR_ENCODING without COLOR_RANGE (iow, supported_ranges being zero) until COLOR_RANGE is better defined than it is at present.
Thoughts?
I'm bringing this up, because the hardware I have has a CSC that accepts BT601 and BT709 formats, controlled by a single bit. Another bit controls whether the CSC produces 0..255 output or 16..235 output. That is then blended/overlaid with the graphics plane (0..255) and sent to the output. Having a "limited range" YUV plane produce 16..235 range output makes it look low-contrast compared to the graphics, which is what would be expected - "16" is not black compared to the black of the graphics in the same way that "235" is not white compared to the graphics.
Drivers are supposed to automatically figure this out by looking at the edid. In i915 we also allow userspace to override this with the "Broadcast RGB" property on the connector. Unfortunately we haven't polished that property yet (not sure what other drivers are doing tbh), so it's only listed in the Documentation/gpu/kms-properties.csv graveyard :-/
In which case, I'd like to implement the COLOR_ENCODING property but not the COLOR_RANGE property until COLOR_RANGE is better defined. Unfortunately, at the moment the choices are to have either both properties or no properties - drm_plane_create_color_properties() doesn't support only creating the encoding property.
Implementing it without it being well defined is a recipe for having a broken UAPI. So, I propose:
Hm maybe I misunderstood, but I thought the COLOR_RANGE is on the input side.
If that's the case, I should force it to only indicate support for limited range, while programming the CSC to produce full range RGB on its output (see below).
Agreed (as far as my understanding of all this goes at least).
And you need to adjust your CSC to make sure the output range is whatever makes things Just Work. Probably better to poke Ville on these details, and then clarify the docs.
It's not possible to arbitarily program the CSC - I have two bits:
- one bit selects whether BT601 or BT709 YUV encoding is used on the CSC input.
- one bit selects whether limited or full range RGB is produced on the CSC output.
Given that I have to assume that the primary plane contains full range RGB values (DRM has no means to communicate from userspace anything else at present) I have to always select full range RGB at the CSC output to be blended with the primary plane.
You could attach the color range stuff also to the primary plane, but I don't think any current userspace is prepared to use it.
I then need some way to know that the TDA998x is being fed by a full range RGB (for the time being, I'm going to assume that's the case) and convert to limited range in the TDA998x if the sink doesn't support full range. I'm proposing to implement your i915 "broadcast rgb" control in TDA998x to allow that to be overridden - maybe that should become a standardised control for HDMI outputs?
Yup that sounds like a very good idea, plus documenting it in
https://dri.freedesktop.org/docs/drm/gpu/drm-kms.html#hdmi-specific-connecto...
Note that at some point we'll have to come up with some new props for specifying the full output colorimetry information and I have a feeling the broadcast rgb prop may get slightly in the way. But we'll have to cross that bridge in i915 anyway so I guess it wouldn't complicate the situation any more if other drivers have this prop as well.
On 04/07/18 12:58, Russell King - ARM Linux wrote:
Hm maybe I misunderstood, but I thought the COLOR_RANGE is on the input side.
If that's the case, I should force it to only indicate support for limited range, while programming the CSC to produce full range RGB on its output (see below).
That should need no forcing. Just set supported_ranges parameter to BIT(DRM_COLOR_YCBCR_LIMITED_RANGE) in drm_plane_create_color_properties() call to create an enum property with only the allowed value.
BR, Jyri
On Tue, Jul 03, 2018 at 05:18:57PM +0100, Russell King - ARM Linux wrote:
Can someone provide a deeper explanation about exactly what this property represents please?
Does this represent the range of YCbCr values _into_ a YCbCr-to-RGB conversion (in other words, the range of values in the framebuffer), or the expected output range from the conversion?
The color_range/encoding props are about the input. The plane output is generally full range RGB, but presumably some driver could choose to use some other internal format as well.
On 03/07/18 19:18, Russell King - ARM Linux wrote:
Can someone provide a deeper explanation about exactly what this property represents please?
Does this represent the range of YCbCr values _into_ a YCbCr-to-RGB conversion (in other words, the range of values in the framebuffer), or the expected output range from the conversion?
Yes, it to describe the YCbCr color encoding used in the buffer given to the plane, nothing more. It should then be up to the driver and display HW to decide what to do with the information. But of course since there is currently no way to tell the range of the RGB buffers used, the working assumption is that the RGB buffers are all full range and the blending is done accordingly.
It should be easy enough to extend the existing enums, or to create completely new ones, for information about the RGB buffers range. Extending has a downside of adding nasty dependency between the framebuffer format and the encoding properties.
The output side is then another matter.
Best regards, Jyri
This matters, because a "limited", (iow, eg, BT601 compliant YCbCr) framebuffer where the Y signal is between 16..235 being displayed on a full-range RGB output would need different conversion from needing a limited-range RGB output.
If it is indeed the output, then why is this a property of the plane? Is that not a property of:
(a) whether the plane is being blended or overlaid onto a graphics plane which uses full-range RGB (b) the properties of the output(s) to which the plane is being displayed.
IOW, it seems that the output of the CSC is more to do with what's downstream of the plane than with the plane itself.
For example, take this situation:
plane 0 - graphics, full range RGB >-- CRTC --> HDMI sink only supporting plane 1 - video, limited range YUV limited range RGB
In order to display the graphics correctly in that scenario, the HDMI output needs to compress the RGB 0-255 range down to 16..236 to be compliant. If the video is limited range, and the CSC produces a limited range RGB output, then plane 1 gets its range further compressed at the HDMI output, which surely is undesirable.
It would surely be better, if it's not possible to map the range of plane 0 to limited range, to instead expand the YUV range and then recompress it at the HDMI output to match the capabilities of the attached source.
It also seems logical that describing the range of the RGB plane would also be sane - if the application is limiting graphics RGB to 16..235, then you'd want the CSC output to do the same and there'd be no need for any range expansion or compression.
I'd personally like drm_plane_create_color_properties() to allow creation of COLOR_ENCODING without COLOR_RANGE (iow, supported_ranges being zero) until COLOR_RANGE is better defined than it is at present.
Thoughts?
I'm bringing this up, because the hardware I have has a CSC that accepts BT601 and BT709 formats, controlled by a single bit. Another bit controls whether the CSC produces 0..255 output or 16..235 output. That is then blended/overlaid with the graphics plane (0..255) and sent to the output. Having a "limited range" YUV plane produce 16..235 range output makes it look low-contrast compared to the graphics, which is what would be expected - "16" is not black compared to the black of the graphics in the same way that "235" is not white compared to the graphics.
dri-devel@lists.freedesktop.org
-
Daniel Vetter -
Jyri Sarha -
Russell King - ARM Linux -
Ville Syrjälä