On Fri, 2017-09-15 at 13:10 +0300, Ville Syrjälä wrote:
> On Tue, Sep 12, 2017 at 04:57:29PM -0700, Dhinakaran Pandiyan wrote:
> > The other instances of link training are protected with
> > connection_mutex, so do the same in check_mst_status() too.
> >
> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/intel_dp.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index aab9ba31f79e..644463ba313e 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -4191,6 +4191,7 @@ static void intel_dp_handle_test_request(struct intel_dp *intel_dp)
> > static int
> > intel_dp_check_mst_status(struct intel_dp *intel_dp)
> > {
> > + struct drm_device *dev = intel_dp_to_dev(intel_dp);
> > bool bret;
> > u8 esi[DP_DPRX_ESI_LEN] = { 0 };
> > int ret = 0;
> > @@ -4205,8 +4206,11 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
> > if (intel_dp->active_mst_links &&
> > !drm_dp_channel_eq_ok(&esi[10], intel_dp->lane_count)) {
> > DRM_DEBUG_KMS("channel EQ not ok, retraining\n");
> > +
> > + drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> > intel_dp_start_link_train(intel_dp);
> > intel_dp_stop_link_train(intel_dp);
> > + drm_modeset_unlock(&dev->mode_config.connection_mutex);
>
> This can deadlock. We should not grab any modeset locks from the
> dig_work. I had some patches at some point to move the link training to
> the hotplug work so SST. I don't think I had the MST side really sorted
> out at any point.
Interesting, the only lock we grab in this path from the work function
is the connection_mutex. So, I am not clear how this will deadlock. This
lock around link training is also at the same depth as the one around
link training in intel_dp_short_pulse(). Wouldn't that also deadlock if
that's the case?
>
> > }
> >
> > DRM_DEBUG_KMS("got esi %3ph\n", esi);
> > --
> > 2.11.0
>
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