[REGRESSION] No image on 4k display port displays connected through usb-c dock in kernel 6.10

[Lin, Wayne]

[Public]

Hi,
Thanks for the report.

Patch fa57924c76d995 ("drm/amd/display: Refactor function dm_dp_mst_is_port_support_mode()")
is kind of correcting problems causing by commit:
4df96ba6676034 ("drm/amd/display: Add timing pixel encoding for mst mode validation")

Sorry if it misses fixes tag and would suggest to backport to fix it. Thanks!

Regards,
Wayne Lin
> -----Original Message-----
> From: kevin at holm.dev <kevin at holm.dev>
> Sent: Sunday, July 28, 2024 12:43 AM
> To: Linux regressions mailing list <regressions at lists.linux.dev>; Deucher,
> Alexander <Alexander.Deucher at amd.com>; Wu, Hersen
> <hersenxs.wu at amd.com>; Lin, Wayne <Wayne.Lin at amd.com>
> Cc: regressions at lists.linux.dev; stable at vger.kernel.org; LKML <linux-
> kernel at vger.kernel.org>; ML dri-devel <dri-devel at lists.freedesktop.org>;
> amd-gfx at lists.freedesktop.org
> Subject: Re: [REGRESSION] No image on 4k display port displays connected
> through usb-c dock in kernel 6.10
>
> > [adding a few people and lists to the recipients]
> >
> > Hi! Thx for your rpeort.
> >
> > On 27.07.24 18:07, kevin at holm.dev wrote:
> >
> > >
> > > Connecting two 4k displays with display port through a lenovo usb-c
> > >
> > >  dock (type 40AS) to a Lenovo P14s Gen 2 (type 21A0) results in no
> > >
> > >  image on the connected displays.
> > >
> > >
> > >
> > >  The CPU in the Lenovo P14s is a 'AMD Ryzen 7 PRO 5850U with Radeon
> > >
> > >  Graphics' and it has no discrete GPU.
> > >
> > >
> > >
> > >  I first noticed the issue with kernel version '6.10.0-arch1-2'
> > >
> > >  provided by arch linux. With the previous kernel version
> > >
> > >  '6.9.10.arch1-1' both connected displays worked normally. I reported
> > >
> > >  the issue in the arch forums at
> > >
> > >  https://bbs.archlinux.org/viewtopic.php?id=297999 and was guided to
> > >
> > >  do a bisection to find the commit that caused the problem. Through
> > >
> > >  testing I identified that the issue is not present in the latest
> > >
> > >  kernel directly compiled from the trovalds/linux git repository.
> > >
> > >
> > >
> > >  With git bisect I identified
> 4df96ba66760345471a85ef7bb29e1cd4e956057
> > >
> >
> > That's 4df96ba6676034 ("drm/amd/display: Add timing pixel encoding for
> >
> > mst mode validation") [v6.10-rc1] from Hersen Wu.
> >
> > Did you try if reverting that commit is possible and might fix the problem?
>
> Reverting is not easily possible:
>
> $ git checkout v6.10
> [...]
> HEAD is now at 0c3836482481 Linux 6.10
>
> $ git revert 4df96ba66760345471a85ef7bb29e1cd4e956057
> Auto-merging
> drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> CONFLICT (content): Merge conflict in
> drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> error: could not revert 4df96ba66760... drm/amd/display: Add timing pixel
> encoding for mst mode validation
>
> I do not know enough to try and solve the conflict myself without breaking
> more things.
>
> >
> > >
> > > as the first bad commit and
> fa57924c76d995e87ca3533ec60d1d5e55769a27
> > >
> >
> > That's fa57924c76d995 ("drm/amd/display: Refactor function
> >
> > dm_dp_mst_is_port_support_mode()") [v6.10-post] from Wayne Lin.
> >
> > >
> > > as the first commit that fixed the problem again.
> > >
> >
> > Hmm, the latter commit does not have a fixes tag and might or might not
> >
> > be to invasive to backport to 6.10. Let's see what the AMD developers say.
> >
> > >
> > > The initial commit only still shows an image on one of the connected
> > >
> > >  4k screens. I have not investigated further to find out at what point
> > >
> > >  both displays stopped showing an image.
> > >
> >
> > Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
> >
> > --
> >
> > Everything you wanna know about Linux kernel regression tracking:
> >
> > https://linux-regtracking.leemhuis.info/about/#tldr
> >
> > If I did something stupid, please tell me, as explained on that page.
> >