[Intel-gfx] [PATCH v2] drm/i915/edp: Do not do link training fallback or prune modes on EDP

[Imre Deak]

On Fri, Jan 19, 2018 at 05:45:16PM +0200, Imre Deak wrote:
> On Thu, Oct 12, 2017 at 12:13:38PM -0700, Manasi Navare wrote:
> > In case of eDP because the panel has a fixed mode, the link rate
> > and lane count at which it is trained corresponds to the link BW
> > required to support the native resolution of the panel. In case of
> > panles with lower resolutions where fewer lanes are hooked up internally,
> > that number is reflected in the MAX_LANE_COUNT DPCD register of the panel.
> > So it is pointless to fallback to lower link rate/lane count in case
> > of link training failure on eDP connector since the lower link BW
> > will not support the native resolution of the panel and we cannot
> > prune the preferred mode on the eDP connector.
> > 
> > In case of Link training failure on the eDP panel, something is wrong
> > in the HW internally and hence driver errors out with a loud
> > and clear DRM_ERROR message.
> > 
> > v2:
> > * Fix the DEBUG_ERROR and add {} in else (Ville Syrjala)
> > 
> > Cc: Clinton Taylor <clinton.a.taylor at intel.com>
> > Cc: Jim Bride <jim.bride at linux.intel.com>
> > Cc: Jani Nikula <jani.nikula at linux.intel.com>
> > Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> > Cc: Dave Airlie <airlied at redhat.com>
> > Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> > Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
> > Reviewed-by: Ville Syrjala <ville.syrjala at linux.intel.com>
> 
> This fell through the cracks, looks like it partially fixes
> https://bugs.freedesktop.org/show_bug.cgi?id=103369
> 
> Why link training fails there is not clear.

Ok, the link training fail turned out to be a race between a modeset
link training and a link retraining called from
runtime_resume->intel_hpd_init->dp_detect. As Ville pointed out that
one was fixed meanwhile by

commit 42e5e65765265485ecf2a480c244d76c2c624449
Author:     Daniel Vetter <daniel.vetter at ffwll.ch>
AuthorDate: Mon Nov 13 17:01:40 2017 +0100
Commit:     Daniel Vetter <daniel.vetter at ffwll.ch>
CommitDate: Thu Nov 23 14:59:07 2017 +0100

    drm/i915: sync dp link status checks against atomic commmits

I merged now this fix to address the other issue, adding the above bug
as reference. Thanks for the patch and the review.

--Imre

> 
> > ---
> >  drivers/gpu/drm/i915/intel_dp_link_training.c | 26 +++++++++++++++++---------
> >  1 file changed, 17 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > index 05907fa..cf8fef8 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > @@ -328,14 +328,22 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
> >  	return;
> >  
> >   failure_handling:
> > -	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);
> > +	/* 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);
> > +	}
> >  	return;
> >  }
> > -- 
> > 2.1.4
> > 
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