[Intel-gfx] Broken DPMS with DisplayPort on CHV (also BYT?)

[Takashi Iwai]

On Thu, 26 Jan 2017 14:58:55 +0100,
Ville Syrjälä wrote:
> 
> On Wed, Jan 25, 2017 at 01:56:35PM +0100, Takashi Iwai wrote:
> > Hi,
> > 
> > we've got a bug report about the blank monitor on Cherry Trail
> > machines.  And, Intel team (Cc'ed) spotted out that this seems
> > triggered by DPMS transition.  A patch like below actually fixes the
> > problem.
> > 
> > Of course it doesn't look like a right "fix".  Do you guys have any
> > hint for further debugging?
> 
> Is it some kind of new fangled MST capable monitor? I've noticed that
> those tend to be super easy to mess up.

The monitors are in Dell team.  Sridhara, could you give details about
the problematic monitors?


> > Some more (not alt-) facts:
> > 
> > - The machine we've tested is a Cherry Trail based box with two
> >   DisplayPorts.  Intel team mentioned that there are other machines
> >   suffering from the same problem.
> 
> Is it really somehow tied to the machine? I would imagine it should
> behave exactly the same way no matter what machine you have.

A good question.  Again the question is delegated to Sridhara :)


> > - With some monitors, the screen remains blank during boot and on X.
> >   This can be cured after "xset dpms force off" and resume, or
> >   reconfiguring via xrandr.
> > 
> > - The issue seems specific to DP connections.  When two (identical)
> >   monitors are connected, only one monitor goes blank.
> 
> Hmm. Have you tried 9f2bdb006a7e ("drm/i915: Prevent PPS stealing
> from a normal DP port on VLV/CHV") ?

No, it's not tested.  I'll prepare a test kernel with it.

Thanks!


Takashi