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

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 2/27/20 7:41 PM, Lyude Paul wrote:
> hi - I almost certainly know the solution to this, the patches that we got
> from amd to do bandwidth checking in the DP MST helpers don't actually work
> correctly in a lot of cases and I need to fix them. I've just been busy on PTO
> and only just got back today, and have been busy with fixing a lot of RHEL
> stuff at the same time. I'll take a closer look at this soonb

Great, I'm a bit worried about the timing for getting this fixed though. We are
not that far into the cycle yet, but still I have the feeling it might be better
to just revert the commit triggering the probably pre-existing problems here
and then queue up the necessary fixes + a new version of that commit when
we have everything in place ?

This way you can take your time to fix this properly instead of having to
do a rush job to fix the regression before 5.6 ships. I think rushing things
never is a good idea. So my vote on this goes to just reverting the commit
triggering this for now and taking our time to get this right.

Regards,

Hans





> 
> On Wed, 2020-02-26 at 16:15 +0100, Hans de Goede 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.
>>
>> 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@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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