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

[Maarten Lankhorst]

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. :)

~Maarten