[Intel-gfx] [PATCH v1] drm/i915: Minor link training logic fixes for dp_mst

[Imre Deak]

On Wed, May 27, 2020 at 11:49:55PM +0300, Imre Deak wrote:
> On Wed, May 27, 2020 at 11:26:49PM +0300, Imre Deak wrote:
> > On Wed, May 27, 2020 at 11:00:22PM +0300, Stanislav Lisovskiy wrote:
> > > First of all *_needs_link_retraining function should return
> > > false is link_train is set to true but not false.
> > > 
> > > Also if we detect channel eq problem when checking mst status
> > > we simply bail out, without setting link_train to false again,
> > > which might end up in a situation that we don't do link retraining
> > > when needed.
> > > 
> > > There were some issues, when we had several problems with dp mst
> > > and at the same time the log was floode by messages about
> > > "channel eq not ok, need retraining" however the actual training
> > > seems to be never done.
> > > 
> > > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/display/intel_dp.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > > index 1768731678a1..9288dc1f8914 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > > @@ -5627,6 +5627,7 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
> > >  			drm_dbg_kms(&i915->drm,
> > >  				    "channel EQ not ok, retraining\n");
> > >  			need_retrain = true;
> > > +			intel_dp->link_trained = false;
> > >  		}
> > >  
> > >  		drm_dbg_kms(&i915->drm, "got esi %3ph\n", esi);
> > > @@ -5654,7 +5655,7 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
> > >  {
> > >  	u8 link_status[DP_LINK_STATUS_SIZE];
> > >  
> > > -	if (!intel_dp->link_trained)
> > > +	if (intel_dp->link_trained)
> > 
> > intel_dp->link_trained is set when we trained the link during a modeset,
> > it doesn't mean that the link status is good, as you seem to interpret
> > it. With this change I don't see how we would retrain the link when this
> > is called from intel_dp_short_pulse(). Could you describe more the
> > failing scenario?
> 
> One reason we wouldn't retrain when needed is that the sink is not seen
> as connected in intel_dp_retrain_link().

But mst is always connected. So maybe intel_dp_needs_link_retrain() does
an early return because intel_dp_get_link_status() or
intel_dp_link_params_valid() fails?

> 
> > 
> > >  		return false;
> > >  
> > >  	/*
> > > -- 
> > > 2.24.1.485.gad05a3d8e5
> > > 
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx