[Intel-gfx] [PATCH] drm/i915/dp_mst: Fix enabling pipe clock for all streams

[Dhinakaran Pandiyan]

On Tue, 2018-09-04 at 16:19 -0700, Rodrigo Vivi wrote:
> On Tue, Sep 04, 2018 at 03:53:51PM -0700, Dhinakaran Pandiyan wrote:
> > On Tuesday, September 4, 2018 5:54:16 AM PDT Imre Deak wrote:
> > > On Tue, Sep 04, 2018 at 03:08:16PM +0300, Jani Nikula wrote:
> > > > On Fri, 31 Aug 2018, Imre Deak <imre.deak at intel.com> wrote:
> > > > > commit afb2c4437dae ("drm/i915/ddi: Push pipe clock enabling
> > > > > to
> > > > > encoders")
> > > > > inadvertently stopped enabling the pipe clock for any DP-MST
> > > > > stream
> > > > > after the first one. It also rearranged the pipe clock
> > > > > enabling wrt.
> > > > > initial MST payload allocation step (which may or may not be
> > > > > a
> > > > > problem, but it's contrary to the spec.).
> > > > > 
> > > > > Fix things by making the above commit truly a non-functional
> > > > > change.
> > > > 
> > > > What kind of MST setups do we have in CI? Why didn't they catch
> > > > this?
> > > 
> > > What we'd need is a dock/other branch device with an DP-MST input
> > > and
> > > two outputs. That would exercise the case that broke here.
> > > 
> > 
> > I had the same question. We have  these two in CI, but both have
> > only one 
> > external display attached.
> > fi-kbl-7560u  Dell XPS 13     Kaby Lake / i7-7560u / Iris Plus
> > Graphics 640 GT3e      
> > eDP, DELL TB16->TB->DP-MST
> > fi-cfl-s3     Intel Coffee Lake-S RVP Coffee Lake     eDP-PSR, DP-
> > MST (HDMI)
> > 
> > Tomi,
> > Is it possible to have another external display connected to one of
> > these?
> 
> or to both of them?!
> 
:) Not sure why I wanted only one of them.


> I'm seeing MST related regressions since 4.16 so I'd like to have few
> different configuration if possible with more than one monitor.

A 4K at 60Hz monitor along with a full-HD (or higher) monitor will be
useful to test the link BW code too. Together, they should be exceeding
the 63 vcpi slot limit. We can then write new IGT's to verify that.


> 
> at least one kind of dock and one kind of chain both with 2 monitors
> plugged in would be good.