[Intel-gfx] [PATCH 09/14] drm/dp/i915: Make clock recovery in the link training compliant with DP Spec 1.2

[Mika Kahola]

On Thu, 2016-09-01 at 15:08 -0700, Manasi Navare wrote:
> From: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> 
> This function cleans up clock recovery loop in link training
> compliant
> tp Dp Spec 1.2. It tries the clock recovery 5 times for the same
> voltage
> or until max voltage swing is reached and removes the additional non
> compliant retries. This function now returns a boolean values based
> on
> if clock recovery passed or failed.
> 
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp_link_training.c | 59 ++++++++++++-----
> ----------
>  1 file changed, 26 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c
> b/drivers/gpu/drm/i915/intel_dp_link_training.c
> index 9145e5a..13a0341 100644
> --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> @@ -117,19 +117,19 @@ static bool
> intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
>  	int lane;
>  
>  	for (lane = 0; lane < intel_dp->lane_count; lane++)
> -		if (intel_dp->train_set[lane] &
> DP_TRAIN_MAX_SWING_REACHED == 0)
> +		if ((intel_dp->train_set[lane] &
> +		     DP_TRAIN_MAX_SWING_REACHED) == 0)
>  			return false;
>  
This function was defined in the previous patch. Do we need to split
this if(...) line into separate lines in this patch? 

>  	return true;
>  }
>  
>  /* Enable corresponding port and start training pattern 1 */
> -static void
> +static bool
>  intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
>  {
> -	int i;
>  	uint8_t voltage;
> -	int voltage_tries, loop_tries;
> +	int voltage_tries, max_vswing_tries;
>  	uint8_t link_config[2];
>  	uint8_t link_bw, rate_select;
>  
> @@ -145,6 +145,7 @@ intel_dp_link_training_clock_recovery(struct
> intel_dp *intel_dp)
>  	if (drm_dp_enhanced_frame_cap(intel_dp->dpcd))
>  		link_config[1] |= DP_LANE_COUNT_ENHANCED_FRAME_EN;
>  	drm_dp_dpcd_write(&intel_dp->aux, DP_LINK_BW_SET,
> link_config, 2);
> +
>  	if (intel_dp->num_sink_rates)
>  		drm_dp_dpcd_write(&intel_dp->aux, DP_LINK_RATE_SET,
>  				  &rate_select, 1);
> @@ -160,58 +161,50 @@ intel_dp_link_training_clock_recovery(struct
> intel_dp *intel_dp)
>  				       DP_TRAINING_PATTERN_1 |
>  				       DP_LINK_SCRAMBLING_DISABLE))
> {
>  		DRM_ERROR("failed to enable link training\n");
> -		return;
> +		return false;
>  	}
>  
> -	voltage = 0xff;
> -	voltage_tries = 0;
> -	loop_tries = 0;
> +	voltage_tries = 1;
> +	max_vswing_tries = 0;
>  	for (;;) {
>  		uint8_t link_status[DP_LINK_STATUS_SIZE];
>  
>  		drm_dp_link_train_clock_recovery_delay(intel_dp-
> >dpcd);
> +
>  		if (!intel_dp_get_link_status(intel_dp,
> link_status)) {
>  			DRM_ERROR("failed to get link status\n");
> -			break;
> +			return false;
>  		}
>  
>  		if (drm_dp_clock_recovery_ok(link_status, intel_dp-
> >lane_count)) {
>  			DRM_DEBUG_KMS("clock recovery OK\n");
> -			break;
> +			return true;
>  		}
>  
> -		/* Check to see if we've tried the max voltage */
> -		if (intel_dp_link_max_vswing_reached(intel_dp)) {
> -			++loop_tries;
> -			if (loop_tries == 5) {
> -				DRM_ERROR("too many full retries,
> give up\n");
> -				intel_dp_dump_link_status(link_statu
> s);
> -				break;
> -			}
> -			intel_dp_reset_link_train(intel_dp,
> -						  DP_TRAINING_PATTER
> N_1 |
> -						  DP_LINK_SCRAMBLING
> _DISABLE);
> -			voltage_tries = 0;
> -			continue;
> +		if (voltage_tries == 5 || max_vswing_tries == 1) {
> +			DRM_DEBUG_KMS("Max. vswing reached or same
> voltage "
> +				      "tried 5 times\n");
> +			return false;
>  		}
I think it would be beneficial to know which one we hit if the clock
recovery fails. Therefore, I would split these debug messages so that
there would be separate debug messages when reaching max vswing or
trying out the same voltage for five times.

>  
> -		/* Check to see if we've tried the same voltage 5
> times */
> -		if ((intel_dp->train_set[0] &
> DP_TRAIN_VOLTAGE_SWING_MASK) == voltage) {
> -			++voltage_tries;
> -			if (voltage_tries == 5) {
> -				DRM_ERROR("too many voltage retries,
> give up\n");
> -				break;
> -			}
> -		} else
> -			voltage_tries = 0;
>  		voltage = intel_dp->train_set[0] &
> DP_TRAIN_VOLTAGE_SWING_MASK;
>  
>  		/* 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;
> +			return false;
>  		}
> +
> +		if ((intel_dp->train_set[0] &
> DP_TRAIN_VOLTAGE_SWING_MASK) ==
> +		    voltage)
> +			++voltage_tries;
> +		else
> +			voltage_tries = 1;
> +
> +		if (intel_dp_link_max_vswing_reached(intel_dp))
> +			++max_vswing_tries;
> +
>  	}
>  }
>  
-- 
Mika Kahola - Intel OTC