[Nouveau] Tracking down severe regression in 5.3-rc4/5.4 for TU116 - assistance needed

[Ilia Mirkin]

Hi Marcin,

You should do a git bisect rather than guessing about commits. I
suspect that searching for "kernel git bisect fedora" should prove
instructive if you're not sure how to do this.

Cheers,

  -ilia

On Mon, Dec 16, 2019 at 11:42 AM Marcin Zajączkowski <mszpak at wp.pl> wrote:
>
> Hi,
>
> I've encountered a severe regression in TU116 (probably also TU117)
> introduced in 5.3-rc4 (valid also for recent 5.4.2) [1]. The system
> usually hangs on the subsequent graphic mode related operation (calling
> xrandr after login is enough) with the following error:
>
> > kernel: nouveau 0000:01:00.0: fifo: SCHED_ERROR 08 []
> ...
> > kernel: nouveau 0000:01:00.0: DRM: failed to idle channel 0 [DRM]
> > kernel: nouveau 0000:01:00.0: i2c: aux 0007: begin idle timeout ffffffff
> > kernel: nouveau 0000:01:00.0: tmr: stalled at ffffffffffffffff
> > kernel: ------------[ cut here ]------------
> > kernel: nouveau 0000:01:00.0: timeout
> > kernel: WARNING: CPU: 10 PID: 384 at drivers/gpu/drm/nouveau/nvkm/subdev/bar/g84.c:35 g84_bar_flush+0xcf/> 0xe0 [nouveau]
>
> (detailed log in a corresponding issue - [1])
>
> With earlier kernels there was no hardware acceleration for NVidia GTX
> 1660 Ti, but at least I could use nouveau to disable it (to save
> battery, trees and lower temperature) or even have an external output
> (with Wayland). Now, the system is unusable with nouveau :(.
>
> I spent some time trying to narrow the scope using on the existing
> kernel builds for Fedora. I was able to determine that the problem was
> introduced between 5.3.0-0.rc3.git1.1 (commit 33920f1ec5bf - works fine)
> and 5.3.0-0.rc4.git0.1 (tag v5.3-rc4 - fails with errors).
>
> It's just a few days (7-11 Aug) and "only" around 250 commits. I went
> through them, but (based on the commits name) I haven't seen any nouveau
> related changes and in general no very suspected drm related changes.
>
> > git log 33920f1ec5bf..v5.3-rc4 --stat
>
>
> Maybe some of more nouveau/drm-experienced developers could take a look
> at that to determine which commit could break it (to make it easier to
> find out what should be fixed to prevent that regression)?
>
>
> [1] -
> https://gitlab.freedesktop.org/xorg/driver/xf86-video-nouveau/issues/516
>
> Thanks in advance
> Marcin
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