On Wed, May 19, 2021 at 12:34:05PM +0300, Pekka Paalanen wrote: > On Wed, 12 May 2021 16:04:16 +0300 > Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > On Wed, May 12, 2021 at 02:06:56PM +0200, Werner Sembach wrote: > > > Hello, > > > > > > In addition to the existing "max bpc", and "Broadcast RGB/output_csc" drm properties I propose 4 new properties: > > > "preferred pixel encoding", "active color depth", "active color range", and "active pixel encoding" > > > > > > > > > Motivation: > > > > > > Current monitors have a variety pixel encodings available: RGB, YCbCr 4:4:4, YCbCr 4:2:2, YCbCr 4:2:0. > > > > > > In addition they might be full or limited RGB range and the monitors accept different bit depths. > > > > > > Currently the kernel driver for AMD and Intel GPUs automatically configure the color settings automatically with little > > > to no influence of the user. However there are several real world scenarios where the user might disagree with the > > > default chosen by the drivers and wants to set his or her own preference. > > > > > > Some examples: > > > > > > 1. While RGB and YCbCr 4:4:4 in theory carry the same amount of color information, some screens might look better on one > > > than the other because of bad internal conversion. The driver currently however has a fixed default that is chosen if > > > available (RGB for Intel and YCbCr 4:4:4 for AMD). The only way to change this currently is by editing and overloading > > > the edid reported by the monitor to the kernel. > > > > > > 2. RGB and YCbCr 4:4:4 need a higher port clock then YCbCr 4:2:0. Some hardware might report that it supports the higher > > > port clock, but because of bad shielding on the PC, the cable, or the monitor the screen cuts out every few seconds when > > > RGB or YCbCr 4:4:4 encoding is used, while YCbCr 4:2:0 might just work fine without changing hardware. The drivers > > > currently however always default to the "best available" option even if it might be broken. > > > > > > 3. Some screens natively only supporting 8-bit color, simulate 10-Bit color by rapidly switching between 2 adjacent > > > colors. They advertise themselves to the kernel as 10-bit monitors but the user might not like the "fake" 10-bit effect > > > and prefer running at the native 8-bit per color. > > > > > > 4. Some screens are falsely classified as full RGB range wile they actually use limited RGB range. This results in > > > washed out colors in dark and bright scenes. A user override can be helpful to manually fix this issue when it occurs. > > > > > > There already exist several requests, discussion, and patches regarding the thematic: > > > > > > - https://gitlab.freedesktop.org/drm/amd/-/issues/476 > > > > > > - https://gitlab.freedesktop.org/drm/amd/-/issues/1548 > > > > > > - https://lkml.org/lkml/2021/5/7/695 > > > > > > - https://lkml.org/lkml/2021/5/11/416 > > > > > ... > > > > Adoption: > > > > > > A KDE dev wants to implement the settings in the KDE settings GUI: > > > https://gitlab.freedesktop.org/drm/amd/-/issues/476#note_912370 > > > > > > Tuxedo Computers (my employer) wants to implement the settings desktop environment agnostic in Tuxedo Control Center. I > > > will start work on this in parallel to implementing the new kernel code. > > > > I suspect everyone would be happier to accept new uapi if we had > > multiple compositors signed up to implement it. > > I think having Weston support for these would be good, but for now it > won't be much of an UI: just weston.ini to set, and the log to see what > happened. > > However, knowing what happened is going to be important for color > calibration auditing: > https://gitlab.freedesktop.org/wayland/weston/-/issues/467 > > Yes, please, very much for read-only properties for the feedback part. > Properties that both userspace and kernel will write are hard to deal > with in general. > > Btw. "max bpc" I can kind of guess that conversion from framebuffer > format to the wire bpc happens automatically and only as the final > step, Well, there could be dithering and whatnot also involved. So it's not super well specified atm either. > but "Broadcast RGB" is more complicated: is the output from the > abstract pixel pipeline sent as-is and "Broadcast RGB" is just another > inforframe bit to the monitor, or does "Broadcast RGB" setting actually > change what happens in the pixel pipeline *and* set infoframe bits? It does indeed compress the actual pixel data. There was once a patch porposed to introduce a new enum value that only sets the infoframe and thus would allow userspace to pass through already limited range data. Shouldn't be hard to resurrect that if needed. > > My vague recollection is that framebuffer was always assumed to be in > full range, and then if "Broadcast RGB" was set to limited range, the > driver would mangle the pixel pipeline to convert from full to limited > range. This means that it would be impossible to have limited range > data in a framebuffer, or there might be a double-conversion by > userspace programming a LUT for limited->full and then the driver > adding full->limited. I'm also confused how full/limited works when > framebuffer is in RGB/YCbCr and the monitor wire format is in RGB/YCbCr > and there may be RGB->YCbCR or YCbCR->RGB conversions going on - or > maybe even FB YCbCR -> RGB -> DEGAMMA -> CTM -> GAMMA -> YCbCR. > > I wish someone drew a picture of the KMS abstract pixel pipeline with > all the existing KMS properties in it. :-) Here's an ugly one for i915: (input RGB vs. YCbCr?) [FB] -> [YCbCr?] -> [YCbCr->RGB conversion ] -> [plane blending] -> ... | [YCbCr color range/encoding] | \ [RGB?] ----------------------------------/ (output RGB limited vs. RGB full vs. YCbCr?) ... -> [DEGAMMA_LUT] -> [CTM] -> [GAMMA_LUT] -> [YCbCr?] -> [RGB->YCbCr conversion ] -> [to port] | [always BT.709/limited range] \ [RGB?] -> ... ... -> [RGB passthrough ] -> [to port] | [Broadcast RGB=full or ] | [Broadcast RGB=auto + IT mode] | \ [RGB full->limited conversion] -> [to port] [Broadcast RGB=limited or ] [Broadcast RGB=auto + CE mode] I guess having something like that in the docs would be nice. Not sure if there's a way to make something that looks decent for html/etc. -- Ville Syrjälä Intel
