[Intel-gfx] [PATCH] drm/i915/dp: Reset link params on connector disconnect

[Ville Syrjälä]

On Thu, Jun 04, 2020 at 09:58:24PM +0300, Ville Syrjälä wrote:
> On Thu, Jun 04, 2020 at 11:52:24AM -0700, Manasi Navare wrote:
> > On Thu, Jun 04, 2020 at 09:38:19PM +0300, Ville Syrjälä wrote:
> > > On Thu, Jun 04, 2020 at 11:35:30AM -0700, Manasi Navare wrote:
> > > > On Thu, Jun 04, 2020 at 06:25:43PM +0300, Ville Syrjälä wrote:
> > > > > On Wed, Jun 03, 2020 at 05:23:59PM -0700, Manasi Navare wrote:
> > > > > > We have noticed that when link training fails the panel
> > > > > > sends a long pulse indicating connector disconnect. In this case
> > > > > > we need to reset the link parameters instead of continuing
> > > > > > to use the fallback parameters since else this long pulse
> > > > > > by the panel followed by a modeset request which was triggered by the userspace
> > > > > > before getting the connector status as disconnected, will
> > > > > > result into a modeset now using lower link rate/lane count values.
> > > > > > 
> > > > > > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1385
> > > > > > Cc: Jani Nikula <jani.nikula at linux.intel.com>
> > > > > > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > > > > Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
> > > > > > ---
> > > > > >  drivers/gpu/drm/i915/display/intel_dp.c | 28 +++++++++++++++++--------
> > > > > >  1 file changed, 19 insertions(+), 9 deletions(-)
> > > > > > 
> > > > > > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > > > > > index 55fda074c0ad..f7af372647dd 100644
> > > > > > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > > > > > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > > > > > @@ -6111,6 +6111,18 @@ intel_dp_unset_edid(struct intel_dp *intel_dp)
> > > > > >  	intel_dp->edid_quirks = 0;
> > > > > >  }
> > > > > >  
> > > > > > +static void
> > > > > > +intel_dp_reset_link_params(struct intel_dp *intel_dp)
> > > > > > +{
> > > > > > +	/* Initial max link lane count */
> > > > > > +	intel_dp->max_link_lane_count = intel_dp_max_common_lane_count(intel_dp);
> > > > > > +
> > > > > > +	/* Initial max link rate */
> > > > > > +	intel_dp->max_link_rate = intel_dp_max_common_rate(intel_dp);
> > > > > > +
> > > > > > +	intel_dp->reset_link_params = false;
> > > > > > +}
> > > > > > +
> > > > > >  static int
> > > > > >  intel_dp_detect(struct drm_connector *connector,
> > > > > >  		struct drm_modeset_acquire_ctx *ctx,
> > > > > > @@ -6139,6 +6151,11 @@ intel_dp_detect(struct drm_connector *connector,
> > > > > >  		memset(&intel_dp->compliance, 0, sizeof(intel_dp->compliance));
> > > > > >  		memset(intel_dp->dsc_dpcd, 0, sizeof(intel_dp->dsc_dpcd));
> > > > > >  
> > > > > > +		/*Reset the immutable VRR Capable property */
> > > > > > +		drm_connector_set_vrr_capable_property(connector,
> > > > > > +						       false);
> > > > > > +		intel_dp_reset_link_params(intel_dp);
> > > > > > +
> > > > > 
> > > > > Why would we care what those are when the sink is disconnected?
> > > > 
> > > > We are noticing this happen in case the panel send this long pulse indicating
> > > > status change to disconnected, while the modeset was already triggered by userspace
> > > > in this case IGT, so the modeset continues right after i915_hotplug_work_fn
> > > > so we need to reset all params which fixes the bug mentioned.
> > > 
> > > Why did the link params get out of whack before hpd in the first place?
> > >
> > 
> > Most of the failures, we see the link training fails due to AUX timeouts and then link params fallback to lower values
> > Then we get this hpd, in this case if we dont reset the param to max values, prev triggered modeset continues
> > with fallback values but since connector probe doesnt happen again through IGT, it tries the same mode
> > with fallback values and return encoder config failure.
> 
> If the link training failed then clearly the sink didn't like us anymore
> anyway. So feels like resetting these here is just shifting some race
> window around a bit, but it could still fail if the sink still doesn't
> like us.
> 
> Would be good if someone was able to figure out why the sink goes bad in
> the first place.

Oh, and don't we now have Imre's "weird hpd happened in the middle of
the test, don't trust the results" thing in igt?

> 
> > 
> > So after reseting the params, the modeset happens with original values and that time link training passes.
> > This is seen in all kms_atomic_transitions IGT tests
> > 
> > Manasi
> >  
> > > > 
> > > > Manasi
> > > > 
> > > > > 
> > > > > >  		if (intel_dp->is_mst) {
> > > > > >  			drm_dbg_kms(&dev_priv->drm,
> > > > > >  				    "MST device may have disappeared %d vs %d\n",
> > > > > > @@ -6152,15 +6169,8 @@ intel_dp_detect(struct drm_connector *connector,
> > > > > >  		goto out;
> > > > > >  	}
> > > > > >  
> > > > > > -	if (intel_dp->reset_link_params) {
> > > > > > -		/* Initial max link lane count */
> > > > > > -		intel_dp->max_link_lane_count = intel_dp_max_common_lane_count(intel_dp);
> > > > > > -
> > > > > > -		/* Initial max link rate */
> > > > > > -		intel_dp->max_link_rate = intel_dp_max_common_rate(intel_dp);
> > > > > > -
> > > > > > -		intel_dp->reset_link_params = false;
> > > > > > -	}
> > > > > > +	if (intel_dp->reset_link_params)
> > > > > > +		intel_dp_reset_link_params(intel_dp);
> > > > > >  
> > > > > >  	intel_dp_print_rates(intel_dp);
> > > > > >  
> > > > > > -- 
> > > > > > 2.19.1
> > > > > 
> > > > > -- 
> > > > > Ville Syrjälä
> > > > > Intel
> > > 
> > > -- 
> > > Ville Syrjälä
> > > Intel
> 
> -- 
> Ville Syrjälä
> Intel
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ville Syrjälä
Intel