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

[Dave Airlie]

On 4 August 2014 18:10, Daniel Vetter <daniel at ffwll.ch> wrote:
> 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

We still check that. if you mean intel_encoders->connectors_active.

Dave.