Re: [PATCH] drm/tegra: Enable cmu for Tegra186 and Tegra194

[Aaron Kling <webgeek1234@gmail.com>]

On Wed, Nov 5, 2025 at 3:28 PM Jasper Korten <jja2000@gmail.com> wrote:
>
> Hi all,
>
> On 11/4/25 19:12, Aaron Kling wrote:
> > On Tue, Nov 4, 2025 at 3:14 AM Thierry Reding <thierry.reding@gmail.com> 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 <thierry.reding@gmail.com> wrote:
> >>>> On Sat, Nov 01, 2025 at 06:15:17PM -0500, Aaron Kling via B4 Relay wrote:
> >>>>> From: Aaron Kling <webgeek1234@gmail.com>
> >>>>>
> >>>>> 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 <webgeek1234@gmail.com>
> >>>>> ---
> >>>>>   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