Re: [PATCH] drm/i915/dp: add lane_count check in intel_dp_check_link_status

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

On Tue, Sep 06, 2016 at 05:43:44PM +0300, Ville Syrjälä wrote:
> On Sat, Aug 27, 2016 at 02:33:25PM +0100, Matthew Auld wrote:
> > Currently it's entirely possible to go through the link training step
> > without first determining the lane_count, which is silly since we end up
> > doing a bunch of aux transfers of size = 0, as highlighted by
> > WARN_ON(!msg->buffer != !msg->size), and can only ever result in a
> > 'failed to update link training' message. This can be observed during
> > intel_dp_long_pulse where we can do the link training step, but before
> > we have had a chance to set the link params. To avoid this we add an
> > extra check for the lane_count in intel_dp_check_link_status, which
> > should prevent us from doing the link training step prematurely.
> > 
> > References: https://bugs.freedesktop.org/show_bug.cgi?id=97344
> > Cc: Jani Nikula <jani.nikula@linux.intel.com>
> > Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index a3c7dd8..0dbb672 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -3927,6 +3927,9 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
> >  	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
> >  		return;
> >  
> > +	if (!intel_dp->lane_count)
> > +		return;
> 
> This pretty much amounts to the same thing that I did with 'active_streams' in 
> my series [1]. The problem is that we need to sync up the state on readout to
> make it really work. Daniel wasn't too happy with my .sync_state() hook, so
> maybe we need something fancier.
> 
> [1] https://patchwork.freedesktop.org/series/10354/

So, looking at some recent logs I see we may hit this WARN spew a *lot*.
So we probably want this patch as a temporary measure. Maybe with
WARN_ONCE() + a comment, eg.

 /*
  * FIXME need to synchronize this sort of
  * stuff properly with hardware readout.
  */

?

> 
> > +
> >  	/* if link training is requested we should perform it always */
> >  	if ((intel_dp->compliance_test_type == DP_TEST_LINK_TRAINING) ||
> >  	    (!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count))) {
> > -- 
> > 2.7.4
> > 
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Ville Syrjälä
> Intel OTC
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ville Syrjälä
Intel OTC
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