[Intel-gfx] [PATCH 1/3] drm/i915: Protect MST retraining with connection_mutex

[Daniel Vetter]

On Wed, Sep 16, 2015 at 01:48:49PM +0200, Maarten Lankhorst wrote:
> Hey,
> 
> Op 03-09-15 om 14:11 schreef Ville Syrjälä:
> > On Thu, Aug 27, 2015 at 06:36:48PM +0300, ville.syrjala at linux.intel.com wrote:
> >> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> >>
> >> Grab the connection_mutex around MSR link retraining to protect it
> >> against a concurrent modeset. We already do the same for SST.
> >>
> >> DP hpd_pulse can still otherwise race against modeset and ->detect(), so
> >> it's not clear what will happen when both want to scribble into eg.
> >> intel_dp->dpcd[] at the same time. But sorting it all out requires way
> >> more thought than I'm willing to expend now.
> > Actually I suppose this might not work out so well after all. I suppose
> > MST depends on short HPDs during modeset due to the sideband stuff.
> >
> > So if we want to grab modeset locks for retraining, I suppose we'd
> > need to move the retraining to happen from .hot_plug() which gets run
> > from the other hotplug work, and so wouldn't interfere with sideband.
> >
> I think it would be better to have a per encoder mutex. In the future we may want to run modeset
> disable/enable async, in which case it may not hold the connection_mutex.
> 
> If we do decide on a separate mutex then it would also be useful to also think about how to
> protect intel_mst_*(dis,en)able_dp. :)

We need to sync re-training with any other modeset work. Which means
another thing to get right for async modesets.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch