[Nouveau] [Bug 75761] weston-launch no output - black screen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=75761

--- Comment #28 from Pekka Paalanen <ppaalanen at gmail.com> ---
I wonder if there are two different bugs in play here.

If you do get the vblank events right, like it sounds that Nerdopolis does
indeed get, then does reverting the blamed nouveau kernel patch make any
difference? I would be surprised if it does make a difference.

This other bug would be, that when Weston changes the video mode, it does not
call drmModeCrtcSetGamma. IIRC Michel Dänzer told me, that not calling that may
lead to black output, if the color translations tables are all zero due not
being explicitly set. So the main question here is, does Weston change the
video mode, or does it use the mode that is already set for fbcon?

Weston code base already has a call to drmModeCrtcSetGamma(), but it is used
only for color managed outputs I think. Yet, it is an example of how to call
it, so if someone having this problem could test that, it would be very useful.
If missing this call is indeed the problem, I think it should be a new Weston
bug report, as the Nouveau patch blamed here should not make a difference
AFAIU.

One more note: if you test reverting the blamed Nouveau patch, make sure your
*both* kernels with and without are built by you and launched the same way, to
make sure that the fbcon video mode is really the same on both. If the fbcon
video mode is different, then that could mask the drmModeCrtcSetGamma issue.

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