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

[Hans de Goede]

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.

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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>