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

[Souza, Jose]

Hi Hans

Just commenting in the "[    3.309061] [drm:intel_dump_pipe_config
[i915]] MST master transcoder: <invalid>" message, it is the expected
behaviour for anything older than Tigerlake, from TGL+ this will be set
in MST mode.

On Wed, 2020-02-26 at 18:52 +0100, Hans de Goede wrote:
> 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
> > > > > 
> > > > > _______________________________________________
> > > > > dri-devel mailing list
> > > > > dri-devel at lists.freedesktop.org
> > > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
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