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