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 5:05 PM, Alex Deucher wrote:
> 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?

I seriously doubt that is the case according to:
https://support.lenovo.com/nl/en/solutions/pd029622

The gen 2 tb3 dock can handle 2 external
displays at 3840*2160 at 60Hz together with the internal
panel being on and both my external displays run at
1920x1080 at 60 so I'm consuming less then half of the
maximum bandwidth.

There definitely is a bug somewhere in the
cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to MST atomic check")
commit (or somewhere else and triggered by that commit).

Regards,

Hans







> 
> 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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>>>> dri-devel at lists.freedesktop.org
>>>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>>>
>>
>