Re: [PATCH v2 1/4] drm/i915/dp: Link train Fallback on eDP only if fallback link BW can fit panel's native mode

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Oct 08, 2018 at 12:23:32PM -0700, Manasi Navare wrote:
> On Mon, Oct 01, 2018 at 07:03:52PM +0300, Ville Syrjälä wrote:
> > On Wed, Sep 12, 2018 at 03:57:16PM -0700, Manasi Navare wrote:
> > > This patch fixes the original commit c0cfb10d9e1de49 ("drm/i915/edp:
> > > Do not do link training fallback or prune modes on EDP") that causes
> > > a blank screen in case of certain eDP panels (Eg: seen on Dell XPS13 9350)
> > > where first link training fails and a retraining is required by falling
> > > back to lower link rate/lane count.
> > > In case of some panels they advertise higher link rate/lane count
> > > than whats required for supporting the panel's native mode.
> > > But we always link train at highest link rate/lane count for eDP
> > > and if that fails we can still fallback to lower link rate/lane count
> > > as long as the fallback link BW still fits the native mode to avoid
> > > pruning the panel's native mode yet retraining at fallback values
> > > to recover from a blank screen.
> > > 
> > > v2:
> > > * Send uevent if link failure on eDP unconditionally
> > > 
> > > Cc: Clinton Taylor <clinton.a.taylor@intel.com>
> > > Cc: Jani Nikula <jani.nikula@linux.intel.com>
> > > Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> > > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107489
> > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105338
> > > Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> > > Tested-by: Alexander Wilson <alexander.wilson@ncf.edu>
> > > ---
> > >  drivers/gpu/drm/i915/intel_dp.c               | 29 +++++++++++++++++++
> > >  drivers/gpu/drm/i915/intel_dp_link_training.c | 26 ++++++-----------
> > >  2 files changed, 38 insertions(+), 17 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > > index 436c22de33b6..e4de5257cd87 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > @@ -557,6 +557,21 @@ static bool intel_dp_link_params_valid(struct intel_dp *intel_dp, int link_rate,
> > >  	return true;
> > >  }
> > >  
> > > +static bool intel_dp_can_link_train_fallback_for_edp(struct intel_dp *intel_dp,
> > > +						     int link_rate,
> > > +						     uint8_t lane_count)
> > > +{
> > > +	struct drm_display_mode *fixed_mode = intel_dp->attached_connector->panel.fixed_mode;
> > 
> > const
> >
> 
> Will add const to the fixed_mode.
>  
> > > +	int mode_rate, max_rate;
> > > +
> > > +	mode_rate = intel_dp_link_required(fixed_mode->clock, 18);
> > > +	max_rate = intel_dp_max_data_rate(link_rate, lane_count);
> > > +	if (mode_rate > max_rate)
> > > +		return false;
> > 
> > I wonder if we should extract this into a helper and share with
> > mode_valid(). Then again, it's just a few lines so maybe not worth it.
> > 
> > > +
> > > +	return true;
> > > +}
> > > +
> > >  int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
> > >  					    int link_rate, uint8_t lane_count)
> > >  {
> > > @@ -566,9 +581,23 @@ int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
> > >  				    intel_dp->num_common_rates,
> > >  				    link_rate);
> > >  	if (index > 0) {
> > > +		if (intel_dp_is_edp(intel_dp) &&
> > > +		    !intel_dp_can_link_train_fallback_for_edp(intel_dp,
> > > +							      intel_dp->common_rates[index - 1],
> > > +							      lane_count)) {
> > > +			DRM_DEBUG_KMS("Retrying Link training for eDP with same parameters\n");
> > > +			return 0;
> > > +		}
> > >  		intel_dp->max_link_rate = intel_dp->common_rates[index - 1];
> > >  		intel_dp->max_link_lane_count = lane_count;
> > >  	} else if (lane_count > 1) {
> > > +		if (intel_dp_is_edp(intel_dp) &&
> > > +		    !intel_dp_can_link_train_fallback_for_edp(intel_dp,
> > > +							      intel_dp_max_common_rate(intel_dp),
> > > +							      lane_count >> 1)) {
> > > +			DRM_DEBUG_KMS("Retrying Link training for eDP with same parameters\n");
> > > +			return 0;
> > > +		}
> > >  		intel_dp->max_link_rate = intel_dp_max_common_rate(intel_dp);
> > >  		intel_dp->max_link_lane_count = lane_count >> 1;
> > 
> > This whole thing is getting a bit messy. I think it would worthwile to
> > rewrite this as something like:
> > 
> > intel_dp_update_link_train_fallback_values(intel_dp)
> > {
> > 	int link_rate = intel_dp->link_rate;
> > 	int lane_count = intel_dp->lane_count;
> > 
> > 	if (intel_dp_get_link_train_fallback_values(intel_dp, &link_rate, &lane_count))
> > 		return -1;
> > 
> > 	if (is_edp() && !edp_can_link_train_thing(link_rate, lane_count)) {
> > 		DRM_DEBUG_KMS("...");
> > 		return 0;
> > 	}
> > 
> > 	intel_dp->max_link_rate = link_rate;
> > 	intel_dp->max_link_lane_count = lane_count;
> > 
> > 	return 0;
> > }
> > 
> > But that can be done later. With the missing const added this patch is
> > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> 
> Yes this can be refactored/reorganized as a follow up patch, also when downclock mode
> checks get in.
> So until then thsi fix is good to be merged right?

Yes.

> 
> Manasi
>  
> > >  	} else {
> > > diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > > index a9f40985a621..30be0e39bd5f 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > > @@ -367,22 +367,14 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
> > >  	return;
> > >  
> > >   failure_handling:
> > > -	/* Dont fallback and prune modes if its eDP */
> > > -	if (!intel_dp_is_edp(intel_dp)) {
> > > -		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
> > > -			      intel_connector->base.base.id,
> > > -			      intel_connector->base.name,
> > > -			      intel_dp->link_rate, intel_dp->lane_count);
> > > -		if (!intel_dp_get_link_train_fallback_values(intel_dp,
> > > -							     intel_dp->link_rate,
> > > -							     intel_dp->lane_count))
> > > -			/* Schedule a Hotplug Uevent to userspace to start modeset */
> > > -			schedule_work(&intel_connector->modeset_retry_work);
> > > -	} else {
> > > -		DRM_ERROR("[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
> > > -			  intel_connector->base.base.id,
> > > -			  intel_connector->base.name,
> > > -			  intel_dp->link_rate, intel_dp->lane_count);
> > > -	}
> > > +	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
> > > +		      intel_connector->base.base.id,
> > > +		      intel_connector->base.name,
> > > +		      intel_dp->link_rate, intel_dp->lane_count);
> > > +	if (!intel_dp_get_link_train_fallback_values(intel_dp,
> > > +						     intel_dp->link_rate,
> > > +						     intel_dp->lane_count))
> > > +		/* Schedule a Hotplug Uevent to userspace to start modeset */
> > > +		schedule_work(&intel_connector->modeset_retry_work);
> > >  	return;
> > >  }
> > > -- 
> > > 2.18.0
> > 
> > -- 
> > Ville Syrjälä
> > Intel

-- 
Ville Syrjälä
Intel
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