Re: [Intel-gfx] [PATCH 4/7] drm/i915: Factor out a helper to disable the DPCD training pattern

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

On Tue, Sep 22, 2020 at 08:41:28PM +0300, Imre Deak wrote:
> On Tue, Sep 22, 2020 at 07:54:20PM +0300, Ville Syrjälä wrote:
> > On Tue, Sep 22, 2020 at 03:51:03PM +0300, Imre Deak wrote:
> > > To prepare for a follow-up LTTPR change factor out a helper to disable
> > > the training pattern in DPCD. We'll need to do this for each LTTPR
> > > (without programming the port to output the idle pattern) when training
> > > in LTTPR non-transparent mode.
> > > 
> > > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > > ---
> > >  .../drm/i915/display/intel_dp_link_training.c | 28 +++++++++++--------
> > >  1 file changed, 16 insertions(+), 12 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > > index 0c3809891bd2..6994a32244dc 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > > @@ -102,30 +102,34 @@ void intel_dp_get_adjust_train(struct intel_dp *intel_dp,
> > >  		intel_dp->train_set[lane] = v | p;
> > >  }
> > >  
> > > +static bool intel_dp_disable_dpcd_training_pattern(struct intel_dp *intel_dp)
> > > +{
> > > +	u8 val = DP_TRAINING_PATTERN_DISABLE;
> > > +
> > > +	return drm_dp_dpcd_write(&intel_dp->aux, DP_TRAINING_PATTERN_SET, &val, 1) == 1;
> > > +}
> > 
> > 
> > > +
> > >  static bool
> > >  intel_dp_set_link_train(struct intel_dp *intel_dp,
> > >  			u8 dp_train_pat)
> > >  {
> > >  	u8 buf[sizeof(intel_dp->train_set) + 1];
> > > -	int ret, len;
> > > +	int len;
> > >  
> > >  	intel_dp_program_link_training_pattern(intel_dp, dp_train_pat);
> > >  
> > > -	buf[0] = dp_train_pat;
> > >  	if ((dp_train_pat & ~DP_LINK_SCRAMBLING_DISABLE) ==
> > > -	    DP_TRAINING_PATTERN_DISABLE) {
> > > +	    DP_TRAINING_PATTERN_DISABLE)
> > >  		/* don't write DP_TRAINING_LANEx_SET on disable */
> > 
> > As mentioned in the other patch I think we're doing things in the wrong
> > order here. I suspect it'll be cleaner to just stop doing
> > intel_dp_set_link_train(DISABLE) entirely and just have a dedicated
> > function for disabling link training. We can then trivially do a
> > followup to swap the order of operations to match the spec.
> 
> intel_dp_disable_dpcd_training_pattern() would be needed after each
> LTTPR link training phase, where the port should not output idle
> patterns, that's the only reason for this change.
> 
> Do you mean to remove intel_dp_stop_link_train() then and do the idle
> pattern programming + corresponding DPCD training pattern disable
> programming at the end of the link training sequence (and remove the
> DP_TRAINING_PATTERN_DISABLE case handling from above)? I agree with
> that, but I see that too as a follow-up material (along with changing
> the order as you suggested).

Yeah, followup shuld be fine. I was just thinking of doing
s/intel_dp_set_link_train(DP_TRAINING_PATTERN_DISABLE)/intel_dp_set_normal_link_train()/
or
s/intel_dp_set_link_train(DP_TRAINING_PATTERN_DISABLE)/intel_dp_disable_link_train()/
or something along those lines.

-- 
Ville Syrjälä
Intel
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