5.6 DP-MST regression: 1 of 2 monitors on TB3 (DP-MST) dock no longer light up

[Alex Deucher]

On Wed, Feb 26, 2020 at 10:43 AM Hans de Goede <hdegoede at redhat.com> wrote:
>
> Hi,
>
> On 2/26/20 4:29 PM, Alex Deucher wrote:
> > On Wed, Feb 26, 2020 at 10:16 AM Hans de Goede <hdegoede at redhat.com> wrote:
> >>
> >> Hi Lyude and everyone else,
> >>
> >> Lyude I'm mailing you about this because you have done a lot of
> >> work on DP MST, but if this rings a bell to anyone else feel
> >> free to weigh in on this.
> >
> > Might be a duplicate of:
> > https://gitlab.freedesktop.org/drm/amd/issues/1052
>
> Looks like you are right, reverting the commit which the bisect
> from that issue points to:
>
> cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to MST atomic check")
>
> Fixes the issue for me. I will add a comment to the issue.
>
> Note I'm using integrated Intel gfx, so that means that this issue
> definitely is not amdgpu specific.
>

I'm not too familiar with the mst code, but I wonder if we were
exceeding the bandwidth limits in some setups and it just happened to
work, but now that we enforcing them, they don't which is correct, but
a regression from some users' perspective?

Alex


> Regards,
>
> Hans
>
>
>
>
> >> I'm currently using a Lenovo X1 7th gen + a Lenovo TB3 gen 2 dock
> >> as my daily rider for testing purposes. When 5.6-rc1 came out I
> >> noticed that only 1 of the 2 1920x1080 at 60 monitors on the dock
> >> lights up.
> >>
> >> There are no kernel errors in the logs, but mutter/gnome-shell says:
> >>
> >> gnome-shell[1316]: Failed to post KMS update: Page flip of 93 failed
> >>
> >> With 93 being the crtc-id of the crtc used for the monitor which is
> >> displaying black. Since then I've waited for 5.6-rc3 hoping that a
> >> fix was already queued up, but 5.6-rc3 still has this problem.
> >>
> >> gnome-shell does behave as if all monitors are connected, so the
> >> monitor is seen, but we are failing to actually send any frames
> >> to it.
> >>
> >> I've put a log collected with drm.debug=0x104 here:
> >> https://fedorapeople.org/~jwrdegoede/drm-debug.log
> >>
> >> This message stands out as pointing to the likely cause of this problem:
> >>
> >> [    3.309061] [drm:intel_dump_pipe_config [i915]] MST master transcoder: <invalid>
> >>
> >> Regards,
> >>
> >> Hans
> >>
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> >
>