Re: [PATCH v4 1/2] drm/i915: DP link training optimization

[Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>]

Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>

On 4/29/2015 11:47 AM, Mika Kahola wrote:
> This is a first of series patches that optimize DP link
> training. The first patch is for eDP only where we reuse
> the previously trained link training values from cache
> i.e. voltage swing and pre-emphasis levels.
>
> In case we are not able to train the link by reusing
> the known values, the link training parameters are set
> to zero and training is restarted.
>
> V2:
> - flag that indicates if DP link is trained and valid
>    renamed from 'link_trained' to 'train_set_valid'
> - removed routine 'intel_dp_reuse_link_train'
>
> V3:
> - rebased against the latest drm-intel-nightly
>
> V4:
> - removed HPD long pulse handling for eDP case to clear the
>    flag that indicates to reuse the current link training
>    parameters. (based on Sivakumar's comment)
>
> Signed-off-by: Mika Kahola <mika.kahola@intel.com>
> ---
>   drivers/gpu/drm/i915/intel_dp.c  | 27 ++++++++++++++++++++++++---
>   drivers/gpu/drm/i915/intel_drv.h |  1 +
>   2 files changed, 25 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 937ba31..e0b35cb 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -3547,7 +3547,8 @@ static bool
>   intel_dp_reset_link_train(struct intel_dp *intel_dp, uint32_t *DP,
>   			uint8_t dp_train_pat)
>   {
> -	memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
> +	if (!intel_dp->train_set_valid)
> +		memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
>   	intel_dp_set_signal_levels(intel_dp, DP);
>   	return intel_dp_set_link_train(intel_dp, DP, dp_train_pat);
>   }
> @@ -3660,6 +3661,23 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
>   			break;
>   		}
>   
> +		/*
> +		 * if we used previously trained voltage and pre-emphasis values
> +		 * and we don't get clock recovery, reset link training values
> +		 */
> +		if (intel_dp->train_set_valid) {
> +			DRM_DEBUG_KMS("clock recovery not ok, reset");
> +			/* clear the flag as we are not reusing train set */
> +			intel_dp->train_set_valid = false;
> +			if (!intel_dp_reset_link_train(intel_dp, &DP,
> +						       DP_TRAINING_PATTERN_1 |
> +						       DP_LINK_SCRAMBLING_DISABLE)) {
> +				DRM_ERROR("failed to enable link training\n");
> +				return;
> +			}
> +			continue;
> +		}
> +
>   		/* Check to see if we've tried the max voltage */
>   		for (i = 0; i < intel_dp->lane_count; i++)
>   			if ((intel_dp->train_set[i] & DP_TRAIN_MAX_SWING_REACHED) == 0)
> @@ -3737,6 +3755,7 @@ intel_dp_complete_link_train(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->train_set_valid = false;
>   			intel_dp_start_link_train(intel_dp);
>   			intel_dp_set_link_train(intel_dp, &DP,
>   						training_pattern |
> @@ -3752,6 +3771,7 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
>   
>   		/* Try 5 times, then try clock recovery if that fails */
>   		if (tries > 5) {
> +			intel_dp->train_set_valid = false;
>   			intel_dp_start_link_train(intel_dp);
>   			intel_dp_set_link_train(intel_dp, &DP,
>   						training_pattern |
> @@ -3773,9 +3793,10 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
>   
>   	intel_dp->DP = DP;
>   
> -	if (channel_eq)
> +	if (channel_eq) {
> +		intel_dp->train_set_valid = is_edp(intel_dp);
>   		DRM_DEBUG_KMS("Channel EQ done. DP Training successful\n");
> -
> +	}
>   }
>   
>   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 43fe003..94197bd 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -736,6 +736,7 @@ struct intel_dp {
>   				     bool has_aux_irq,
>   				     int send_bytes,
>   				     uint32_t aux_clock_divider);
> +	bool train_set_valid;
>   
>   	/* Displayport compliance testing */
>   	unsigned long compliance_test_type;

-- 
regards,
Sivakumar

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