On Tue, Jan 27, 2026 at 4:32 AM Thierry Reding <[email protected]> wrote: > > On Tue, Jan 27, 2026 at 01:12:54PM +0900, Mikko Perttunen wrote: > > On Thursday, January 22, 2026 2:08 AM Kurt Kiefer wrote: > > > > > > > On Dec 8, 2025, at 8:23 PM, Aaron Kling <[email protected]> wrote: > > > > > > > > On Wed, Nov 5, 2025 at 3:28 PM Jasper Korten <[email protected]> wrote: > > > >> > > > >> Hi all, > > > >> > > > >> On 11/4/25 19:12, Aaron Kling wrote: > > > >>> On Tue, Nov 4, 2025 at 3:14 AM Thierry Reding > > > >>> <[email protected]> wrote: > > > >>>> On Mon, Nov 03, 2025 at 12:39:57PM -0600, Aaron Kling wrote: > > > >>>>> On Mon, Nov 3, 2025 at 5:54 AM Thierry Reding > > > >>>>> <[email protected]> wrote: > > > >>>>>> On Sat, Nov 01, 2025 at 06:15:17PM -0500, Aaron Kling via B4 Relay > > > >>>>>> wrote: > > > >>>>>>> From: Aaron Kling <[email protected]> > > > >>>>>>> > > > >>>>>>> Without the cmu, nvdisplay will display colors that are notably > > > >>>>>>> darker > > > >>>>>>> than intended. The vendor bootloader and the downstream display > > > >>>>>>> driver > > > >>>>>>> enable the cmu and sets a sRGB table. Loading that table here > > > >>>>>>> results in > > > >>>>>>> the intended colors. > > > >>>>>>> > > > >>>>>>> Signed-off-by: Aaron Kling <[email protected]> > > > >>>>>>> --- > > > >>>>>>> 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 > > > >>>>> nvdisplay > > > >>>>> looks like right now. It's nigh unusably dark. When booted into > > > >>>>> Android with a tv launcher that has a black background, as is > > > >>>>> default > > > >>>>> 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 > > > >>>> what > > > >>>> 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 > > > >> Aaron > > > >> 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. > > > >>>> > > > >>>> 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? > > > >>> > > > >>> My current setup is a rack of units plugged via hdmi to a kvm which is > > > >>> 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 to > > > >>> allow for a bisect. > > > >>> > > > >>> 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. > > > >> > > > >> 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. > > > >> > > > >> > > > >> 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. > > > > > > > > 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. > > > > > > > > Aaron > > > > > > > > > > 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. > > > > > > 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". > > > > > > 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. > > > > > > 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. > > > > > > 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 output. > > > > The colorspace the display expects from the incoming data is specified > > in the 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 lot of fields > > set at the default. > > > > Currently we're advertising: > > * colorimetry = no data -> for HD resolutions, use Rec. 709 primaries. > > These are the same as sRGB. > > * itc = 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 gamma. sRGB gamma is slightly different, and setting itc = > > true would hint the display towards using sRGB gamma. > > > > However, what seems clear to me is that the display would be expecting > > nonlinear 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 discussed). > > I think ideally we want to hook this up to the DRM color management > facilities, so that it can both be properly reported and configured > at runtime.
That would be ideal yes. But I don't have nearly the knowledge of DRM or nvdisplay to wire this up. Is there someone at Nvidia that can make time to do so? > Obviously we also want to make sure that the output pixels match what > is advertised via the AVI infoframe. Looks like there's concensus that > enabling the output LUT is the correct way to do that. If more fully featured CMU support can't be done in a reasonable timeframe, I can address the earlier review comments and coordinate with Kurt to replicate this for DP, then send a v2. Aaron
