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The vendor bootloader and the downstream display d= river > >>>>>>> enable the cmu and sets a sRGB table. Loading that table here res= ults in > >>>>>>> the intended colors. > >>>>>>>=20 > >>>>>>> Signed-off-by: Aaron Kling > >>>>>>> --- > >>>>>>> drivers/gpu/drm/tegra/dc.h | 13 +++ > >>>>>>> drivers/gpu/drm/tegra/sor.c | 206 ++++++++++++++++++++++++++++++= ++++++++++++++ > >>>>>>> 2 files changed, 219 insertions(+) > >>>>>> What does "darker than intended" mean? Who defines the intention? = How do > >>>>>> we know what the intention is? What this patch ultimately seems to= be > >>>>>> doing is define sRGB to be the default colorspace. Is that always = the > >>>>>> right default choice? What if people want to specify a different > >>>>>> colorspace? > >>>>> I reported this issue almost a month ago. See kernel lore [0] and > >>>>> freedesktop issue [1]. The pictures in the latter show what nvdispl= ay > >>>>> looks like right now. It's nigh unusably dark. When booted into > >>>>> Android with a tv launcher that has a black background, as is defau= lt > >>>>> for LineageOS, it is really hard to read anything. Is it correct as= a > >>>>> default? Well, cboot hardcodes this, so... presumably? It would be > >>>>> more ideal to expose this and csc to userspace, but I'm not sure if > >>>>> drm has a standardized interface for that or if tegra would have to > >>>>> make something vendor specific. I think that would be a separate > >>>>> change concept compared to setting this default, though. > >>>> The reason I'm asking is because I don't recall ever seeing "broken" > >>>> colors like you do. So I suspect that this may also be related to wh= at > >>>> display is connected, or the mode that we're setting. > >> I have tried it on both a MacroSilicon HDMI capture card and an Arzopa > >> Z1FC 1080p portable monitor and run into the same darker colors. Both > >> have in common that they use HDMI which seems to line up with what Aar= on > >> is reporting. I do not have an eDP display to test or another carrier > >> board with a different display out to test. > >>>> It could perhaps > >>>> also be related to what infoframes we're sending and how these are > >>>> supported/interpreted by the attached display. > >>>>=20 > >>>> All of that is to say that maybe this looks broken on the particular > >>>> setup that you have but may works fine on other setups. Changing the > >>>> default may fix your setup and break others. > >>> Do you have a device set up so you can check? Or does the regression > >>> test bench have a display that can be forwarded? > >>>=20 > >>> My current setup is a rack of units plugged via hdmi to a kvm which i= s > >>> then plugged to a pikvm. I also observed this issue before I had this > >>> setup, plugged directly to a 1080p monitor. I have not checked > >>> displayport. I can cycle through a couple other displays without this > >>> patch to see if I get any other result. I am fairly certain I have > >>> consistently seen this issue since I started trying to work with > >>> tegra-drm on kernel 6.1 or maybe even 5.15. I've never seen it work t= o > >>> allow for a bisect. > >>>=20 > >>> I am in contact with one other person with a tx2 devkit, who > >>> replicated the issue when I asked. Who plans to reply to this thread > >>> with setup info later. > >>=20 > >> For reference, I am said person. I have a Jetson TX2 Devkit that uses > >> the P2771 Device Tree. I'm running a Fedora distrokernel with no > >> additional patches applied by myself. I have personally noticed the > >> issue to at least be present on 6.14.5 and 6.17.4. > >>=20 > >>=20 > >> I'm currently not at home to take screenshots with and without the > >> submitted patch, but will be able to do it tomorrownight or friday. > >=20 > > Any further thoughts from the maintainers on this patch? As far as I > > know, this is an issue for all users, at the very least on hdmi. > >=20 > > Aaron > >=20 >=20 > I can confirm that I have the same issue on a DisplayPort output of t194. > IMO, this patch will need to be reworked a bit to enable the CMU for this > output as well. I hacked this change in for DisplayPort, and then it > functioned as intended there as well. >=20 > I've traced back to the reason this is necessary. The DC hub driver is > applying an sRGB degamma for every RGB plane (presumably for blending), > and then nothing reapplies the EOTF later on. Without gamma correction > in places where it is expected, images are going to look "too dark". >=20 > Which does raise the point that there is an alternative implementation > where we do not degamma RGB planes in the first place. But this may have > unintended consequences when it comes to composition. >=20 > The SOR does not appear to handle YCbCr outputs at this time, so enabling > the CMU assuming an sRGB EOTF seems like a reasonable path here, to me. >=20 > Kurt I tested this patch locally and did some investigation. Can confirm that on= my Jetson AGX Xavier, this patch (or disabling degamma) fixes the color ou= tput. The colorspace the display expects from the incoming data is specified in t= he AVI infoframe. This is generated in tegra_sor_hdmi_setup_avi_infoframe, = which calls into drm_hdmi_avi_infoframe_from_display_mode, which leaves a l= ot of fields set at the default. Currently we're advertising: * colorimetry =3D no data -> for HD resolutions, use Rec. 709 primaries. Th= ese are the same as sRGB. * itc =3D false -> NOT IT content. My understanding (based on some LLM research and otherwise) is that this is= likely to result in the display expecting Rec. 709 colors with Rec. 709 ga= mma. sRGB gamma is slightly different, and setting itc =3D true would hint = the display towards using sRGB gamma. However, what seems clear to me is that the display would be expecting nonl= inear data, so enabling gamma conversion at the output LUT seems correct to= me. So this patch would be a clear improvement (with the fixes already dis= cussed). Mikko