[Intel-gfx] [PATCH v5 3/3] drm/i915: DP channel EQ check for use of DP link training optimization

[Mika Kahola]

On Mon, 2016-01-04 at 18:53 +0200, Ville Syrjälä wrote:
> On Mon, Jan 04, 2016 at 06:44:09PM +0200, Ville Syrjälä wrote:
> > On Mon, Jan 04, 2016 at 01:21:24PM +0200, Mika Kahola wrote:
> > > Don't use DP link training optimization if channel EQ is not ok. It has
> > > been reported that in case of failure in channel EQ check the link training
> > > optimization can be enabled and therefore may not be able to reuse the
> > > previously computed drive current and pre-emphasis levels.
> > > 
> > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91393
> > > Signed-off-by: Mika Kahola <mika.kahola at intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_dp.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > > index 3137187..0cd1ccb 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > @@ -4354,6 +4354,7 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
> > >  		(!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count))) {
> > >  		DRM_DEBUG_KMS("%s: channel EQ not ok, retraining\n",
> > >  			      intel_encoder->base.name);
> > > +		intel_dp->train_set_valid = false;
> > >  		intel_dp_start_link_train(intel_dp);
> > >  		intel_dp_stop_link_train(intel_dp);
> > >  	}
> > 
> > Should do the same for the MST case I suppose?
> 
> Also I wonder if we shold maintain some sort of blacklist of unstable
> vswing/preemph settings so that we wouldn't even try to retrain with
> values we know to be of questionable quality...
I think it would be quite tricky to maintain such a list. There is quite
a bunch of source/sink combinations out there. For eDP this would be
easier if we could first learn which vsing/preemph settings are unusable
and maintain the blacklist based on that.

Cheers,
Mika 
> 
> > 
> > > -- 
> > > 1.9.1
> > 
> > -- 
> > Ville Syrjälä
> > Intel OTC
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> > Intel-gfx at lists.freedesktop.org
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>