[Intel-gfx] [PATCH 10/14] drm/i915: Make DP link training channel equalization DP 1.2 Spec compliant

[Pandiyan, Dhinakaran]

On Fri, 2016-09-02 at 14:20 +0300, Mika Kahola wrote:
> On Thu, 2016-09-01 at 15:08 -0700, Manasi Navare wrote:
> > Fix the number of tries in channel euqalization link training
> > sequence
> > according to DP 1.2 Spec. It returns a boolean depending on channel
> > equalization pass or failure.
> > 
> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> > Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp_link_training.c | 57 ++++++++++-------
> > ----------
> >  drivers/gpu/drm/i915/intel_drv.h              |  1 +
> >  2 files changed, 22 insertions(+), 36 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c
> > b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > index 13a0341..07f0159 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > @@ -240,12 +240,12 @@ static u32 intel_dp_training_pattern(struct
> > intel_dp *intel_dp)
> >  	return training_pattern;
> >  }
> >  
> > -static void
> > +static bool
> >  intel_dp_link_training_channel_equalization(struct intel_dp
> > *intel_dp)
> >  {
> > -	bool channel_eq = false;
> > -	int tries, cr_tries;
> > +	int tries;
> >  	u32 training_pattern;
> > +	uint8_t link_status[DP_LINK_STATUS_SIZE];
> >  
> >  	training_pattern = intel_dp_training_pattern(intel_dp);
> >  
> > @@ -254,20 +254,11 @@
> > intel_dp_link_training_channel_equalization(struct intel_dp
> > *intel_dp)
> >  				     training_pattern |
> >  				     DP_LINK_SCRAMBLING_DISABLE)) {
> >  		DRM_ERROR("failed to start channel equalization\n");
> > -		return;
> > +		return false;
> >  	}
> >  
> > -	tries = 0;
> > -	cr_tries = 0;
> > -	channel_eq = false;
> > -	for (;;) {
> > -		uint8_t link_status[DP_LINK_STATUS_SIZE];
> > -
> > -		if (cr_tries > 5) {
> > -			DRM_ERROR("failed to train DP, aborting\n");
> > -			intel_dp_dump_link_status(link_status);
> > -			break;
> > -		}
> > +	intel_dp->channel_eq_status = false;
> > +	for (tries = 0; tries < 5; tries++) {
> >  
> >  		drm_dp_link_train_channel_eq_delay(intel_dp->dpcd);
> >  		if (!intel_dp_get_link_status(intel_dp,
> > link_status)) {
> > @@ -278,44 +269,38 @@
> > intel_dp_link_training_channel_equalization(struct intel_dp
> > *intel_dp)
> >  		/* Make sure clock is still ok */
> >  		if (!drm_dp_clock_recovery_ok(link_status,
> >  					      intel_dp->lane_count)) 
> > {
> > -			intel_dp_link_training_clock_recovery(intel_
> > dp);
> > -			intel_dp_set_link_train(intel_dp,
> > -						training_pattern |
> > -						DP_LINK_SCRAMBLING_D
> > ISABLE);
> > -			cr_tries++;
> > -			continue;
> > +			intel_dp_dump_link_status(link_status);
> > +			DRM_DEBUG_KMS("Clock recovery check failed,
> > cannot "
> > +				      "continue channel
> > equalization\n");
> > +			break;
> >  		}
> This clock recovery check got me thinking. Do we really need to check
> if clock recovery is still ok within a loop? Could we move this outside
> the loop and return early if we have failed in clock recovery? One idea
> that I have in mind is that we wouldn't need to enter in channel
> equalization if we have failed with clock recovery earlier.
> 

Looks like we do. This check helps us to break out of the loop for link
rate reduction after adjusting drive setting. 


> >  
> >  		if (drm_dp_channel_eq_ok(link_status,
> >  					 intel_dp->lane_count)) {
> > -			channel_eq = true;
> > +			intel_dp->channel_eq_status = true;
> > +			DRM_DEBUG_KMS("Channel EQ done. DP Training
> > "
> > +				      "successful\n");
> >  			break;
> >  		}
> >  
> > -		/* Try 5 times, then try clock recovery if that
> > fails */
> > -		if (tries > 5) {
> > -			intel_dp_link_training_clock_recovery(intel_
> > dp);
> > -			intel_dp_set_link_train(intel_dp,
> > -						training_pattern |
> > -						DP_LINK_SCRAMBLING_D
> > ISABLE);
> > -			tries = 0;
> > -			cr_tries++;
> > -			continue;
> > -		}
> > -
> >  		/* Update training set as requested by target */
> >  		intel_get_adjust_train(intel_dp, link_status);
> >  		if (!intel_dp_update_link_train(intel_dp)) {
> >  			DRM_ERROR("failed to update link
> > training\n");
> >  			break;
> >  		}
> > -		++tries;
> > +	}
> > +
> > +	/* Try 5 times, else fail and try at lower BW */
> > +	if (tries == 5) {
> > +		intel_dp_dump_link_status(link_status);
> > +		DRM_DEBUG_KMS("Channel equalization failed 5
> > times\n");
> >  	}
> >  
> >  	intel_dp_set_idle_link_train(intel_dp);
> >  
> > -	if (channel_eq)
> > -		DRM_DEBUG_KMS("Channel EQ done. DP Training
> > successful\n");
> > +	return intel_dp->channel_eq_status;
> > +
> >  }
> >  
> >  void intel_dp_stop_link_train(struct intel_dp *intel_dp)
> > diff --git a/drivers/gpu/drm/i915/intel_drv.h
> > b/drivers/gpu/drm/i915/intel_drv.h
> > index efcd80b..e5bc976 100644
> > --- a/drivers/gpu/drm/i915/intel_drv.h
> > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > @@ -878,6 +878,7 @@ struct intel_dp {
> >  	bool link_mst;
> >  	bool has_audio;
> >  	bool detect_done;
> > +	bool channel_eq_status;
> >  	enum hdmi_force_audio force_audio;
> >  	bool limited_color_range;
> >  	bool color_range_auto;