Re: [Intel-gfx] [PATCH RESEND] drm/i915: Revert DisplayPort fast link training feature

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 20 Jun 2016, Mika Kahola <mika.kahola@intel.com> wrote:
> It has been found out that in some HW combination the DisplayPort
> fast link training feature caused screen flickering. Let's revert
> this feature for now until we can ensure that the feature works for
> all platforms.
>
> This is a manual revert of commits 5fa836a9d859 ("drm/i915: DP link
> training optimization") and 4e96c97742f4 ("drm/i915: eDP link training
> optimization").
>
> Fixes: 5fa836a9d859 ("drm/i915: DP link training optimization")
> Fixes: 4e96c97742f4 ("drm/i915: eDP link training optimization")
> Cc: <stable@vger.kernel.org> # v4.2+
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91393
> Reviewed-by: Jani Nikula <jani.nikula@intel.com>
> Signed-off-by: Mika Kahola <mika.kahola@intel.com>

Pushed to drm-intel-next-queued, thanks for the patch.

BR,
Jani.

> ---
>  drivers/gpu/drm/i915/intel_dp.c               |  3 ---
>  drivers/gpu/drm/i915/intel_dp_link_training.c | 26 ++------------------------
>  drivers/gpu/drm/i915/intel_drv.h              |  2 --
>  3 files changed, 2 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index be08351..3cdea4d7a 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4621,9 +4621,6 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
>  	intel_display_power_get(dev_priv, power_domain);
>  
>  	if (long_hpd) {
> -		/* indicate that we need to restart link training */
> -		intel_dp->train_set_valid = false;
> -
>  		intel_dp_long_pulse(intel_dp->attached_connector);
>  		if (intel_dp->is_mst)
>  			ret = IRQ_HANDLED;
> diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> index 0b8eefc..60fb39c 100644
> --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> @@ -85,8 +85,7 @@ static bool
>  intel_dp_reset_link_train(struct intel_dp *intel_dp,
>  			uint8_t dp_train_pat)
>  {
> -	if (!intel_dp->train_set_valid)
> -		memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
> +	memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
>  	intel_dp_set_signal_levels(intel_dp);
>  	return intel_dp_set_link_train(intel_dp, dp_train_pat);
>  }
> @@ -161,23 +160,6 @@ intel_dp_link_training_clock_recovery(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_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)
> @@ -284,7 +266,6 @@ 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->train_set_valid = false;
>  			intel_dp_link_training_clock_recovery(intel_dp);
>  			intel_dp_set_link_train(intel_dp,
>  						training_pattern |
> @@ -301,7 +282,6 @@ intel_dp_link_training_channel_equalization(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_link_training_clock_recovery(intel_dp);
>  			intel_dp_set_link_train(intel_dp,
>  						training_pattern |
> @@ -322,10 +302,8 @@ intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp)
>  
>  	intel_dp_set_idle_link_train(intel_dp);
>  
> -	if (channel_eq) {
> -		intel_dp->train_set_valid = true;
> +	if (channel_eq)
>  		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 0c1dc9b..9257f08 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -894,8 +894,6 @@ struct intel_dp {
>  	/* This is called before a link training is starterd */
>  	void (*prepare_link_retrain)(struct intel_dp *intel_dp);
>  
> -	bool train_set_valid;
> -
>  	/* Displayport compliance testing */
>  	unsigned long compliance_test_type;
>  	unsigned long compliance_test_data;

-- 
Jani Nikula, Intel Open Source Technology Center