[Intel-gfx] [PATCH 1/3] drm/i915/dp: Fix link retraining comment in intel_dp_long_pulse()

[Ville Syrjälä]

On Fri, Sep 07, 2018 at 03:39:24PM +0300, Jani Nikula wrote:
> On Thu, 06 Sep 2018, Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com> wrote:
> > Comment claims link needs to be retrained because the connected sink raised
> > a long pulse to indicate link loss. If the sink did so,
> > intel_dp_hotplug() would have handled link retraining. Looking at the
> > logs in Bugzilla referenced in commit '3cf71bc9904d ("drm/i915: Re-apply
> > Perform link quality check, unconditionally during long pulse"")', the
> > issue is that the sink does not trigger an interrupt. We want the
> > ->detect() from user space to check link status and retrain. Ville's
> > review for the original patch also indicates the same root cause.
> >
> > I have also renamed long_pulse() to full_detect().
> 
> Since intel_dp_detect() doesn't actually do *anything* except skip
> detect sometimes, I think "full detect" is a misnomer.
> 
> Arguably you could merge intel_dp_long_pulse() into its only caller,
> intel_dp_detect(), and do an early return on skipping detect. You have
> to look at the functions, and wonder if the current split is the right
> one.

That's pretty much what I suggested earlier. Although someone should
double check to make sure the detect_done flag even makes sense these
days. Maybe it does, maybe it doesn't, I don't recall.

> 
> Please let others chime in too before making changes.
> 
> BR,
> Jani.
> 
> 
> >
> > Cc: Lyude Paul <lyude at redhat.com>
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Cc: Jani Nikula <jani.nikula at linux.intel.com>
> > Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > Cc: Jan-Marek Glogowski <glogow at fbihome.de>
> > References: 3cf71bc9904d ("drm/i915: Re-apply "Perform link quality check, unconditionally during long pulse"")
> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 17 +++++------------
> >  1 file changed, 5 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 436c22de33b6..befdaa076d8c 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -5012,7 +5012,7 @@ intel_dp_unset_edid(struct intel_dp *intel_dp)
> >  }
> >  
> >  static int
> > -intel_dp_long_pulse(struct intel_connector *connector,
> > +intel_dp_full_detect(struct intel_connector *connector,
> >  		    struct drm_modeset_acquire_ctx *ctx)
> >  {
> >  	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
> > @@ -5074,16 +5074,8 @@ intel_dp_long_pulse(struct intel_connector *connector,
> >  		goto out;
> >  	} else {
> >  		/*
> > -		 * If display is now connected check links status,
> > -		 * there has been known issues of link loss triggering
> > -		 * long pulse.
> > -		 *
> > -		 * Some sinks (eg. ASUS PB287Q) seem to perform some
> > -		 * weird HPD ping pong during modesets. So we can apparently
> > -		 * end up with HPD going low during a modeset, and then
> > -		 * going back up soon after. And once that happens we must
> > -		 * retrain the link to get a picture. That's in case no
> > -		 * userspace component reacted to intermittent HPD dip.
> > +		 * Check link status in case the link went out of
> > +		 * synchronization and the sink did not tell us.
> >  		 */
> >  		struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
> >  
> > @@ -5149,7 +5141,8 @@ intel_dp_detect(struct drm_connector *connector,
> >  				return ret;
> >  		}
> >  
> > -		status = intel_dp_long_pulse(intel_dp->attached_connector, ctx);
> > +		status = intel_dp_full_detect(intel_dp->attached_connector,
> > +					      ctx);
> >  	}
> >  
> >  	intel_dp->detect_done = false;
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center

-- 
Ville Syrjälä
Intel