Re: [PATCH v3 4/4] drm/i915: Implement Link Rate fallback on Link training failure

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

On Wed, 02 Nov 2016, Manasi Navare <manasi.d.navare@intel.com> wrote:
> If link training at a link rate optimal for a particular
> mode fails during modeset's atomic commit phase, then we
> let the modeset complete and then retry. We save the link rate
> value at which link training failed, update the link status property
> to "BAD" and use a lower link rate to prune the modes. It will redo
> the modeset on the current mode at lower link rate or if the current
> mode gets pruned due to lower link constraints then, it will send a
> hotplug uevent for userspace to handle it.
>
> This is also required to pass DP CTS tests 4.3.1.3, 4.3.1.4,
> 4.3.1.6.
>
> v3:
> * Set link status property to BAd unconditionally (Jani Nikula)
> * Dont use two separate variables link_train_failed and link_status
> to indicate same thing (Jani Nikula)
> v2:
> * Squashed a few patches (Jani Nikula)
>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c           |  7 +++
>  drivers/gpu/drm/i915/intel_ddi.c              | 22 ++++++++-
>  drivers/gpu/drm/i915/intel_dp.c               | 70 ++++++++++++++++++++++++---
>  drivers/gpu/drm/i915/intel_dp_link_training.c | 12 +++--
>  drivers/gpu/drm/i915/intel_drv.h              |  6 ++-
>  5 files changed, 105 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 75ad01d..94b0b3a 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -519,6 +519,13 @@ static int handle_conflicting_encoders(struct drm_atomic_state *state,
>  					       connector_state);
>  		if (ret)
>  			return ret;
> +
> +		if (connector->state->crtc) {
> +			crtc_state = drm_atomic_get_existing_crtc_state(state,
> +									connector->state->crtc);
> +			if (connector->link_status == DRM_MODE_LINK_STATUS_BAD)
> +				crtc_state->connectors_changed = true;
> +		}
>  	}

Could this be a separate patch? Anyway needs to be posted on dri-devel.

>  
>  	/*
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index 938ac4d..a59f8d2 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -1684,6 +1684,8 @@ static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
>  	struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
>  	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
>  	enum port port = intel_ddi_get_encoder_port(encoder);
> +	struct intel_connector *intel_connector = intel_dp->attached_connector;
> +	struct drm_connector *connector = &intel_connector->base;
>  
>  	intel_dp_set_link_params(intel_dp, link_rate, lane_count,
>  				 link_mst);
> @@ -1694,7 +1696,25 @@ static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
>  	intel_prepare_dp_ddi_buffers(encoder);
>  	intel_ddi_init_dp_buf_reg(encoder);
>  	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
> -	intel_dp_start_link_train(intel_dp);
> +	if (!intel_dp_start_link_train(intel_dp)) {
> +		DRM_DEBUG_KMS("Link Training failed at link rate = %d, lane count = %d",
> +			      link_rate, lane_count);
> +		connector->link_status = DRM_MODE_LINK_STATUS_BAD;

Why does this not use intel_dp_set_link_status_property()?

> +		intel_dp_get_link_train_fallback_values(intel_dp, link_rate,
> +							lane_count);
> +		/* Schedule a Hotplug Uevent to userspace to start modeset */
> +		schedule_work(&intel_connector->modeset_retry_work);
> +	} else {
> +		DRM_DEBUG_KMS("Link Training Passed at Link Rate = %d, Lane count = %d",
> +			      link_rate, lane_count);
> +		intel_dp->fallback_link_rate_index = -1;
> +		intel_dp->fallback_link_rate = 0;
> +		intel_dp->fallback_lane_count = 0;
> +		connector->link_status = DRM_MODE_LINK_STATUS_GOOD;
> +		intel_dp_set_link_status_property(connector,
> +						  DRM_MODE_LINK_STATUS_GOOD);
> +	}
> +
>  	if (port != PORT_A || INTEL_GEN(dev_priv) >= 9)
>  		intel_dp_stop_link_train(intel_dp);
>  }
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index fb4fcdd..659b17f 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -310,9 +310,6 @@ void intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
>  	int common_len;
>  	int link_rate_index = -1;
>  
> -	if (!intel_dp->link_train_failed)
> -		return;
> -

You add this in an earlier patch and now remove it?

>  	common_len = intel_dp_common_rates(intel_dp, common_rates);
>  	link_rate_index = intel_dp_link_rate_index(intel_dp,
>  						   common_rates,
> @@ -327,7 +324,6 @@ void intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
>  		intel_dp->fallback_lane_count = lane_count >> 1;
>  	} else {
>  		DRM_ERROR("Link Training Unsuccessful\n");
> -		intel_dp->link_train_failed = false;
>  	}
>  }
>  
> @@ -354,8 +350,14 @@ void intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
>  		target_clock = fixed_mode->clock;
>  	}
>  
> -	max_link_clock = intel_dp_max_link_rate(intel_dp);
> -	max_lanes = intel_dp_max_lane_count(intel_dp);
> +	/* Prune the modes using the fallback link rate/lane count */
> +	if (connector->link_status == DRM_MODE_LINK_STATUS_BAD) {
> +		max_link_clock = intel_dp->fallback_link_rate;
> +		max_lanes = intel_dp->fallback_lane_count;
> +	} else {
> +		max_link_clock = intel_dp_max_link_rate(intel_dp);
> +		max_lanes = intel_dp_max_lane_count(intel_dp);
> +	}
>  
>  	max_rate = intel_dp_max_data_rate(max_link_clock, max_lanes);
>  	mode_rate = intel_dp_link_required(target_clock, 18);
> @@ -1593,6 +1595,7 @@ static int intel_dp_compute_bpp(struct intel_dp *intel_dp,
>  	enum port port = dp_to_dig_port(intel_dp)->port;
>  	struct intel_crtc *intel_crtc = to_intel_crtc(pipe_config->base.crtc);
>  	struct intel_connector *intel_connector = intel_dp->attached_connector;
> +	struct drm_connector *connector = &intel_connector->base;
>  	int lane_count, clock;
>  	int min_lane_count = 1;
>  	int max_lane_count = intel_dp_max_lane_count(intel_dp);
> @@ -1640,6 +1643,12 @@ static int intel_dp_compute_bpp(struct intel_dp *intel_dp,
>  	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLCLK)
>  		return false;
>  
> +	/* Fall back to lower link rate in case of failure in previous modeset */
> +	if (connector->link_status == DRM_MODE_LINK_STATUS_BAD) {
> +		min_lane_count = max_lane_count = intel_dp->fallback_lane_count;
> +		min_clock = max_clock = intel_dp->fallback_link_rate_index;
> +	}
> +
>  	DRM_DEBUG_KMS("DP link computation with max lane count %i "
>  		      "max bw %d pixel clock %iKHz\n",
>  		      max_lane_count, common_rates[max_clock],
> @@ -4423,6 +4432,12 @@ static bool intel_digital_port_connected(struct drm_i915_private *dev_priv,
>  		intel_dp->compliance_test_active = 0;
>  		intel_dp->compliance_test_type = 0;
>  		intel_dp->compliance_test_data = 0;
> +		intel_dp->fallback_link_rate_index = -1;
> +		intel_dp->fallback_link_rate = 0;
> +		intel_dp->fallback_lane_count = 0;
> +		connector->link_status = DRM_MODE_LINK_STATUS_GOOD;
> +		intel_dp_set_link_status_property(connector,
> +						  DRM_MODE_LINK_STATUS_GOOD);

Seems like it would be a good idea to have this
intel_dp_set_link_status_property() helper set connector->link_status
too.

>  
>  		if (intel_dp->is_mst) {
>  			DRM_DEBUG_KMS("MST device may have disappeared %d vs %d\n",
> @@ -4514,6 +4529,11 @@ static bool intel_digital_port_connected(struct drm_i915_private *dev_priv,
>  	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n",
>  		      connector->base.id, connector->name);
>  
> +	/* If this is a retry due to link trianing failure */
> +	if (status == connector_status_connected &&
> +	    connector->link_status == DRM_MODE_LINK_STATUS_BAD)
> +		return status;
> +
>  	/* If full detect is not performed yet, do a full detect */
>  	if (!intel_dp->detect_done)
>  		status = intel_dp_long_pulse(intel_dp->attached_connector);
> @@ -5692,6 +5712,40 @@ static bool intel_edp_init_connector(struct intel_dp *intel_dp,
>  	return false;
>  }
>  
> +static void intel_dp_modeset_retry_work_fn(struct work_struct *work)
> +{
> +	struct intel_connector *intel_connector;
> +	struct drm_connector *connector;
> +	struct drm_display_mode *mode;
> +	bool verbose_prune = true;
> +
> +	intel_connector = container_of(work, typeof(*intel_connector),
> +				       modeset_retry_work);
> +	connector = &intel_connector->base;
> +
> +	/* Grab the locks before changing connector property*/
> +	mutex_lock(&connector->dev->mode_config.mutex);
> +	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n", connector->base.id,
> +		      connector->name);
> +	list_for_each_entry(mode, &connector->modes, head) {
> +		mode->status = intel_dp_mode_valid(connector,
> +						   mode);
> +	}
> +	drm_mode_prune_invalid(connector->dev, &connector->modes,
> +			       verbose_prune);
> +
> +	/* Set connector link status to BAD and send a Uevent to notify
> +	 * userspace to do a modeset.
> +	 */
> +	connector->link_status = DRM_MODE_LINK_STATUS_BAD;
> +	intel_dp_set_link_status_property(connector,
> +					  DRM_MODE_LINK_STATUS_BAD);
> +	mutex_unlock(&connector->dev->mode_config.mutex);
> +
> +	/* Send Hotplug uevent so userspace can reprobe */
> +	drm_kms_helper_hotplug_event(connector->dev);
> +}
> +
>  bool
>  intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
>  			struct intel_connector *intel_connector)
> @@ -5704,6 +5758,10 @@ static bool intel_edp_init_connector(struct intel_dp *intel_dp,
>  	enum port port = intel_dig_port->port;
>  	int type;
>  
> +	/* Initialize the work for modeset in case of link train failure */
> +	INIT_WORK(&intel_connector->modeset_retry_work,
> +		  intel_dp_modeset_retry_work_fn);
> +
>  	if (WARN(intel_dig_port->max_lanes < 1,
>  		 "Not enough lanes (%d) for DP on port %c\n",
>  		 intel_dig_port->max_lanes, port_name(port)))
> diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> index 0048b52..10f81ab 100644
> --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> @@ -310,9 +310,15 @@ void intel_dp_stop_link_train(struct intel_dp *intel_dp)
>  				DP_TRAINING_PATTERN_DISABLE);
>  }
>  
> -void
> +bool
>  intel_dp_start_link_train(struct intel_dp *intel_dp)
>  {
> -	intel_dp_link_training_clock_recovery(intel_dp);
> -	intel_dp_link_training_channel_equalization(intel_dp);
> +	bool ret;
> +
> +	if (intel_dp_link_training_clock_recovery(intel_dp)) {
> +		ret = intel_dp_link_training_channel_equalization(intel_dp);
> +		if (ret)
> +			return true;
> +	}
> +	return false;
>  }
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index bc25b2b..c0378a9 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -312,6 +312,9 @@ struct intel_connector {
>  	void *port; /* store this opaque as its illegal to dereference it */
>  
>  	struct intel_dp *mst_port;
> +
> +	/* Work struct to schedule a uevent on link train failure */
> +	struct work_struct modeset_retry_work;
>  };
>  
>  struct dpll {
> @@ -900,7 +903,6 @@ struct intel_dp {
>  	int fallback_link_rate;
>  	uint8_t fallback_lane_count;
>  	int fallback_link_rate_index;
> -	bool link_train_failed;
>  	uint8_t sink_count;
>  	bool link_mst;
>  	bool has_audio;
> @@ -1402,7 +1404,7 @@ void intel_dp_set_link_params(struct intel_dp *intel_dp,
>  			      bool link_mst);
>  void intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
>  					     int link_rate, uint8_t lane_count);
> -void intel_dp_start_link_train(struct intel_dp *intel_dp);
> +bool intel_dp_start_link_train(struct intel_dp *intel_dp);
>  void intel_dp_stop_link_train(struct intel_dp *intel_dp);
>  void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode);
>  void intel_dp_encoder_reset(struct drm_encoder *encoder);

-- 
Jani Nikula, Intel Open Source Technology Center
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