[Intel-gfx] [PATCH] drm/i915: Add a bit of locking to intel_dp_hpd_pulse()

[Daniel Vetter]

On Fri, Aug 01, 2014 at 02:55:22PM +0300, Ville Syrjälä wrote:
> On Thu, Jul 31, 2014 at 08:59:08PM +1000, Dave Airlie wrote:
> > On 31 July 2014 17:37, Daniel Vetter <daniel at ffwll.ch> wrote:
> > > On Thu, Jul 31, 2014 at 1:49 AM, Dave Airlie <airlied at gmail.com> wrote:
> > >> Daniel, the only way intel_dp->is_mst can get reset is inside this path.
> > >
> > > Ok, so that one should be safe. Then I guess we can just push the
> > > locking down into the respective non-mst leafs (since atm we do
> > > link-retraining without any locking, which isn't good). And it needs
> > > to be dev->mode_config.mutex, not connection mutex.
> 
> Why that? We can't be doing a modeset w/o connection_mutex so that
> seems like it should be enough. Well, there's also dpms which leaves
> the crtc<->encoder<->connector links intact but that too takes
> connection_mutex currently.
> 
> > 
> > I'd like to know why we do link training at this point though as well,
> > adding locking is required of course, I was just going to wrap the
> > short irq call to the link status check with the lock, but I think it
> > should be possible to push it down further,
> 
> I don't really know why the sink generates the hpd when we turn off the
> port, but that doesn't really matter I think. We need to be prepared for
> hpds at any time.
> 
> intel_dp_check_link_status() just checks if there's a crtc, which there
> is (either the old one or the new one, depending on how far along the
> modeset path we are I guess), and then it just checks
> drm_dp_channel_eq_ok() which says false since the link was turned off,
> and then it proceeds to retrain the link.
> 
> Maybe it should also check crtc->active? Though that itself won't 
> eliminate the problem unless the locking gets fixed somehow.

We check encoder->connectors_active, which is equivalent.
-Daniel

> 
> > 
> > I'm not sure how vague the spec is on what should happen on HPDs, but
> > if we drop the port clock we obviously will lose the link, but we
> > should also know not to be retraining it at that point anyways.
> > 
> > Dave.
> 
> -- 
> Ville Syrjälä
> Intel OTC

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch