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

[Dhinakaran Pandiyan]

On Fri, 2018-09-07 at 17:32 +0300, Ville Syrjälä wrote:
> 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. 
I had mixed feelings when I wrote it, but merging the functions does
sound like a better idea now.

> 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.
It doesn't afaict. The only place where detect_done gets set to true is
followed by resetting of the flag to false.

-DK
> 
> > 
> > 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
> 
>