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

[Manasi Navare]

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.

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