Am 19.05.21 um 15:49 schrieb Ville Syrjälä: > 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. For the time being I try to keep the functionality of Broadcast RGB the same and just port it over to AMDGPU, but i haven't looked into it in detail yet. > >> 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. >
