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Date:   Mon, 12 Mar 2018 15:05:22 -0700
From:   Manasi Navare <manasi.d.navare@intel.com>
To:     Lyude Paul <lyude@redhat.com>
Cc:     intel-gfx@lists.freedesktop.org, David Airlie <airlied@linux.ie>,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        Rodrigo Vivi <rodrigo.vivi@intel.com>
Subject: Re: [PATCH v3 5/5] drm/i915: Implement proper fallback training for
 MST
Message-ID: <20180312220522.GC3022@intel.com>
References: <20180308232421.14049-1-lyude@redhat.com>
 <20180309213232.19855-1-lyude@redhat.com>
 <20180309213232.19855-5-lyude@redhat.com>
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In-Reply-To: <20180309213232.19855-5-lyude@redhat.com>
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On Fri, Mar 09, 2018 at 04:32:31PM -0500, Lyude Paul wrote:
> For a while we actually haven't had any way of retraining MST links with
> fallback link parameters like we do with SST. While uncommon, certain
> setups such as my Caldigit TS3 + EVGA MST hub require this since
> otherwise, they end up getting stuck in an infinite MST retraining loop.
> 
> MST retraining is somewhat different then SST retraining. While it's
> possible during the normal link retraining sequence for a hub to indicate
> bad link status, it's also possible for a hub to only indicate this
> status through ESI messages and it's possible for this to happen after
> the initial link training succeeds. This can lead to a pattern that
> looks like this:
> 
> - Train MST link
> - Training completes successfully
> - MST hub sets Channel EQ failed bit in ESI
> - Retraining starts
> - Retraining completes successfully
> - MST hub sets Channel EQ failed bit in ESI again
> - Rinse and repeat
> 
> In these situations, we need to be able to actually trigger fallback
> link training from the ESI handler as well, along with using the ESI
> handler during retraining to figure out whether or not our retraining
> actually succeeded.
> 
> This gets a bit more complicated since we have to ensure that we don't
> block the ESI handler at all while doing retraining. If we do, due to
> DisplayPort's general issues with being sensitive to IRQ latency most
> MST hubs will just stop responding to us if their interrupts aren't
> handled in a timely manner.
> 
> So: move retraining into it's own seperate handler. Running in a
> seperate handler allows us to avoid stalling the ESI during link
> retraining, and we can have the ESI signal that the channel EQ bit was
> cleared through a simple completion struct. Additionally, we take care
> to stick as much of this into the SST retraining path as possible since
> sharing is caring.
>

Thanks for the patch for MST retraining. So just to confirm my understanding of the
cases where MS retraining is handled:
1. On link the first link training failure during the modeset, this would just
use SST modeset retry function and set the link status to BAD through drm_dp_mst_topology_mgr_lower_link_rate()

2. In case that it suceeds here but then loses synchronization in between, that time it will send IRQ_HPD and
indicate this through ESI and the way its handled is through intel_dp_mst_check_link_status() and then through
the separate mst_retrain_link work. And this time we first try to retrain at the current values for 5 times and
then fallback and retry by sending hotplug uevent.

Is this correct?

Manasi

> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Cc: Manasi Navare <manasi.d.navare@intel.com>
> Cc: Ville Syrj?l? <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c     | 342 +++++++++++++++++++++++++++---------
>  drivers/gpu/drm/i915/intel_dp_mst.c |  42 ++++-
>  drivers/gpu/drm/i915/intel_drv.h    |   8 +
>  3 files changed, 302 insertions(+), 90 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 5645a194de92..7626652732b6 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -45,6 +45,8 @@
>  
>  #define DP_DPRX_ESI_LEN 14
>  
> +#define DP_MST_RETRAIN_TIMEOUT (msecs_to_jiffies(100))
> +
>  /* Compliance test status bits  */
>  #define INTEL_DP_RESOLUTION_SHIFT_MASK	0
>  #define INTEL_DP_RESOLUTION_PREFERRED	(1 << INTEL_DP_RESOLUTION_SHIFT_MASK)
> @@ -4224,6 +4226,118 @@ static void intel_dp_handle_test_request(struct intel_dp *intel_dp)
>  		DRM_DEBUG_KMS("Could not write test response to sink\n");
>  }
>  
> +/* Get a mask of the CRTCs that are running on the given intel_dp struct. For
> + * MST, this returns a crtc mask containing all of the CRTCs driving
> + * downstream sinks, for SST it just returns a mask of the attached
> + * connector's CRTC.
> + */
> +int
> +intel_dp_get_crtc_mask(struct intel_dp *intel_dp)
> +{
> +	struct drm_device *dev = dp_to_dig_port(intel_dp)->base.base.dev;
> +	struct drm_connector *connector;
> +	struct drm_connector_state *conn_state;
> +	struct intel_connector *intel_connector;
> +	struct drm_crtc *crtc;
> +	int crtc_mask = 0;
> +
> +	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
> +
> +	if (intel_dp->is_mst) {
> +		struct drm_connector_list_iter conn_iter;
> +
> +		drm_connector_list_iter_begin(dev, &conn_iter);
> +		for_each_intel_connector_iter(intel_connector, &conn_iter) {
> +			if (intel_connector->mst_port != intel_dp)
> +				continue;
> +
> +			conn_state = intel_connector->base.state;
> +			if (!conn_state->crtc)
> +				continue;
> +
> +			crtc_mask |= drm_crtc_mask(conn_state->crtc);
> +		}
> +		drm_connector_list_iter_end(&conn_iter);
> +	} else {
> +		connector = &intel_dp->attached_connector->base;
> +		crtc = connector->state->crtc;
> +
> +		if (crtc)
> +			crtc_mask |= drm_crtc_mask(crtc);
> +	}
> +
> +	return crtc_mask;
> +}
> +
> +static bool
> +intel_dp_needs_link_retrain(struct intel_dp *intel_dp,
> +			    const u8 esi[DP_DPRX_ESI_LEN])
> +{
> +	u8 buf[max(DP_LINK_STATUS_SIZE, DP_DPRX_ESI_LEN)];
> +	const u8 *link_status = NULL;
> +
> +	if (intel_dp->is_mst) {
> +		if (!intel_dp->active_mst_links)
> +			return false;
> +		if (intel_dp->mst_link_is_bad)
> +			return false;
> +
> +		if (esi) {
> +			link_status = &esi[10];
> +		} else {
> +			/* We're not running from the ESI handler, so wait a
> +			 * little bit to see if the ESI handler lets us know
> +			 * that the link status is OK
> +			 */
> +			if (wait_for_completion_timeout(
> +				&intel_dp->mst_retrain_completion,
> +				DP_MST_RETRAIN_TIMEOUT))
> +				return false;
> +		}
> +	} else {
> +		if (intel_dp->link_trained)
> +			return false;
> +		if (!intel_dp_get_link_status(intel_dp, buf))
> +			return false;
> +
> +		link_status = buf;
> +	}
> +
> +	/*
> +	 * Validate the cached values of intel_dp->link_rate and
> +	 * intel_dp->lane_count before attempting to retrain.
> +	 */
> +	if (!intel_dp_link_params_valid(intel_dp, intel_dp->link_rate,
> +					intel_dp->lane_count))
> +		return false;
> +
> +	if (link_status) {
> +		return !drm_dp_channel_eq_ok(link_status,
> +					     intel_dp->lane_count);
> +	} else {
> +		return true;
> +	}
> +}
> +
> +static inline void
> +intel_dp_mst_check_link_status(struct intel_dp *intel_dp,
> +			       const u8 esi[DP_DPRX_ESI_LEN])
> +{
> +	if (intel_dp_needs_link_retrain(intel_dp, esi)) {
> +		DRM_DEBUG_KMS("Channel EQ failing\n");
> +
> +		if (!work_busy(&intel_dp->mst_retrain_work)) {
> +			reinit_completion(&intel_dp->mst_retrain_completion);
> +			schedule_work(&intel_dp->mst_retrain_work);
> +			DRM_DEBUG_KMS("Retraining started\n");
> +		}
> +	} else if (work_busy(&intel_dp->mst_retrain_work) &&
> +		   !completion_done(&intel_dp->mst_retrain_completion)) {
> +		DRM_DEBUG_KMS("Channel EQ stable\n");
> +		complete_all(&intel_dp->mst_retrain_completion);
> +	}
> +}
> +
>  static int
>  intel_dp_check_mst_status(struct intel_dp *intel_dp)
>  {
> @@ -4237,14 +4351,7 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
>  		bret = intel_dp_get_sink_irq_esi(intel_dp, esi);
>  go_again:
>  		if (bret == true) {
> -
> -			/* check link status - esi[10] = 0x200c */
> -			if (intel_dp->active_mst_links &&
> -			    !drm_dp_channel_eq_ok(&esi[10], intel_dp->lane_count)) {
> -				DRM_DEBUG_KMS("channel EQ not ok, retraining\n");
> -				intel_dp_start_link_train(intel_dp);
> -				intel_dp_stop_link_train(intel_dp);
> -			}
> +			intel_dp_mst_check_link_status(intel_dp, esi);
>  
>  			DRM_DEBUG_KMS("got esi %3ph\n", esi);
>  			ret = drm_dp_mst_hpd_irq(&intel_dp->mst_mgr, esi, &handled);
> @@ -4281,29 +4388,6 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
>  	return -EINVAL;
>  }
>  
> -static bool
> -intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
> -{
> -	u8 link_status[DP_LINK_STATUS_SIZE];
> -
> -	if (!intel_dp->link_trained)
> -		return false;
> -
> -	if (!intel_dp_get_link_status(intel_dp, link_status))
> -		return false;
> -
> -	/*
> -	 * Validate the cached values of intel_dp->link_rate and
> -	 * intel_dp->lane_count before attempting to retrain.
> -	 */
> -	if (!intel_dp_link_params_valid(intel_dp, intel_dp->link_rate,
> -					intel_dp->lane_count))
> -		return false;
> -
> -	/* Retrain if Channel EQ or CR not ok */
> -	return !drm_dp_channel_eq_ok(link_status, intel_dp->lane_count);
> -}
> -
>  /*
>   * If display is now connected check links status,
>   * there has been known issues of link loss triggering
> @@ -4319,64 +4403,78 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
>  int intel_dp_retrain_link(struct intel_encoder *encoder,
>  			  struct drm_modeset_acquire_ctx *ctx)
>  {
> -	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
> +	struct drm_device *dev = encoder->base.dev;
> +	struct drm_i915_private *dev_priv = to_i915(dev);
>  	struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
> -	struct intel_connector *connector = intel_dp->attached_connector;
> -	struct drm_connector_state *conn_state;
> -	struct intel_crtc_state *crtc_state;
> -	struct intel_crtc *crtc;
> +	struct drm_crtc *crtc;
> +	struct intel_crtc *intel_crtc;
> +	int crtc_mask, retry_count = 0;
>  	int ret;
>  
> -	/* FIXME handle the MST connectors as well */
> -
> -	if (!connector || connector->base.status != connector_status_connected)
> -		return 0;
> -
>  	ret = drm_modeset_lock(&dev_priv->drm.mode_config.connection_mutex,
>  			       ctx);
>  	if (ret)
>  		return ret;
>  
> -	conn_state = connector->base.state;
> -
> -	crtc = to_intel_crtc(conn_state->crtc);
> -	if (!crtc)
> -		return 0;
> +	crtc_mask = intel_dp_get_crtc_mask(intel_dp);
> +	for_each_intel_crtc_mask(dev, intel_crtc, crtc_mask) {
> +		struct drm_crtc_state *crtc_state;
> +		struct intel_crtc_state *intel_crtc_state;
>  
> -	ret = drm_modeset_lock(&crtc->base.mutex, ctx);
> -	if (ret)
> -		return ret;
> +		crtc = &intel_crtc->base;
> +		ret = drm_modeset_lock(&crtc->mutex, ctx);
> +		if (ret)
> +			return ret;
>  
> -	crtc_state = to_intel_crtc_state(crtc->base.state);
> +		crtc_state = crtc->state;
> +		intel_crtc_state = to_intel_crtc_state(crtc_state);
> +		WARN_ON(!intel_crtc_has_dp_encoder(intel_crtc_state));
>  
> -	WARN_ON(!intel_crtc_has_dp_encoder(crtc_state));
> +		if (crtc_state->commit &&
> +		    !try_wait_for_completion(&crtc_state->commit->hw_done))
> +			return 0;
> +	}
>  
> -	if (!crtc_state->base.active)
> +	if (!intel_dp_needs_link_retrain(intel_dp, NULL))
>  		return 0;
>  
> -	if (conn_state->commit &&
> -	    !try_wait_for_completion(&conn_state->commit->hw_done))
> -		return 0;
> +	for_each_intel_crtc_mask(dev, intel_crtc, crtc_mask) {
> +		intel_set_cpu_fifo_underrun_reporting(
> +		    dev_priv, intel_crtc->pipe, false);
>  
> -	if (!intel_dp_needs_link_retrain(intel_dp))
> -		return 0;
> +		if (intel_crtc->config->has_pch_encoder) {
> +			intel_set_pch_fifo_underrun_reporting(
> +			    dev_priv, intel_crtc_pch_transcoder(intel_crtc),
> +			    false);
> +		}
> +	}
>  
> -	/* Suppress underruns caused by re-training */
> -	intel_set_cpu_fifo_underrun_reporting(dev_priv, crtc->pipe, false);
> -	if (crtc->config->has_pch_encoder)
> -		intel_set_pch_fifo_underrun_reporting(dev_priv,
> -						      intel_crtc_pch_transcoder(crtc), false);
> +	do {
> +		if (++retry_count > 5) {
> +			DRM_DEBUG_KMS("Too many retries, can't retrain\n");
> +			return -EINVAL;
> +		}
>  
> -	intel_dp_start_link_train(intel_dp);
> -	intel_dp_stop_link_train(intel_dp);
> +		intel_dp_start_link_train(intel_dp);
> +		intel_dp_stop_link_train(intel_dp);
> +	} while (intel_dp_needs_link_retrain(intel_dp, NULL));
> +
> +	/* Wait for things to become stable */
> +	for_each_intel_crtc_mask(dev, intel_crtc, crtc_mask)
> +		intel_wait_for_vblank(dev_priv, intel_crtc->pipe);
>  
> -	/* Keep underrun reporting disabled until things are stable */
> -	intel_wait_for_vblank(dev_priv, crtc->pipe);
> +	/* Now that we know everything is OK, finally re-enable underrun
> +	 * reporting */
> +	for_each_intel_crtc_mask(dev, intel_crtc, crtc_mask) {
> +		intel_set_cpu_fifo_underrun_reporting(
> +		    dev_priv, intel_crtc->pipe, true);
>  
> -	intel_set_cpu_fifo_underrun_reporting(dev_priv, crtc->pipe, true);
> -	if (crtc->config->has_pch_encoder)
> -		intel_set_pch_fifo_underrun_reporting(dev_priv,
> -						      intel_crtc_pch_transcoder(crtc), true);
> +		if (intel_crtc->config->has_pch_encoder) {
> +			intel_set_pch_fifo_underrun_reporting(
> +			    dev_priv, intel_crtc_pch_transcoder(intel_crtc),
> +			    true);
> +		}
> +	}
>  
>  	return 0;
>  }
> @@ -4402,6 +4500,10 @@ static bool intel_dp_hotplug(struct intel_encoder *encoder,
>  
>  	changed = intel_encoder_hotplug(encoder, connector);
>  
> +	/* We don't want to end up trying to retrain MST links! */
> +	if (encoder && enc_to_intel_dp(&encoder->base)->is_mst)
> +		return changed;
> +
>  	drm_modeset_acquire_init(&ctx, 0);
>  
>  	for (;;) {
> @@ -4478,7 +4580,7 @@ intel_dp_short_pulse(struct intel_dp *intel_dp)
>  	}
>  
>  	/* defer to the hotplug work for link retraining if needed */
> -	if (intel_dp_needs_link_retrain(intel_dp))
> +	if (intel_dp_needs_link_retrain(intel_dp, NULL))
>  		return false;
>  
>  	if (intel_dp->compliance.test_type == DP_TEST_LINK_TRAINING) {
> @@ -6266,25 +6368,98 @@ static bool intel_edp_init_connector(struct intel_dp *intel_dp,
>  	return false;
>  }
>  
> +static void intel_dp_mst_retrain_link_work(struct work_struct *work)
> +{
> +	struct drm_modeset_acquire_ctx ctx;
> +	struct intel_dp *intel_dp = container_of(work, typeof(*intel_dp),
> +						 mst_retrain_work);
> +	struct intel_encoder *intel_encoder = &dp_to_dig_port(intel_dp)->base;
> +	struct drm_device *dev = intel_encoder->base.dev;
> +	int ret;
> +	bool had_error = false;
> +
> +	drm_modeset_acquire_init(&ctx, 0);
> +
> +	for (;;) {
> +		ret = intel_dp_retrain_link(intel_encoder, &ctx);
> +		if (ret == -EDEADLK) {
> +			drm_modeset_backoff(&ctx);
> +			continue;
> +		}
> +
> +		break;
> +	}
> +	if (!ret) {
> +		DRM_DEBUG_KMS("Retrain complete\n");
> +		goto out;
> +	} else if (ret == -EIO) {
> +		DRM_ERROR("IO error with sink during retrain? Aborting\n");
> +		had_error = true;
> +		goto out;
> +	}
> +
> +	DRM_DEBUG_KMS("Retraining failed with %d, marking link status as bad\n",
> +		      ret);
> +
> +	/* We ran out of retries, if the sink hasn't changed the link rate in
> +	 * it's dpcd yet force us to fallback to a lower link rate/count */
> +	if (ret == -EINVAL) {
> +		ret = intel_dp_get_dpcd(intel_dp);
> +		if (!ret) {
> +			DRM_ERROR("IO error while reading dpcd from sink\n");
> +			had_error = true;
> +			goto out;
> +		}
> +
> +		if (intel_dp->link_rate == intel_dp_max_link_rate(intel_dp) &&
> +		    intel_dp->lane_count == intel_dp_max_lane_count(intel_dp)) {
> +			intel_dp_get_link_train_fallback_values(
> +			    intel_dp, intel_dp_max_link_rate(intel_dp),
> +			    intel_dp_max_lane_count(intel_dp));
> +		}
> +	}
> +
> +	intel_dp->mst_link_is_bad = true;
> +	intel_dp->mst_bw_locked = false;
> +	schedule_work(&intel_dp->modeset_retry_work);
> +out:
> +	drm_modeset_drop_locks(&ctx);
> +	drm_modeset_acquire_fini(&ctx);
> +	if (had_error)
> +		drm_kms_helper_hotplug_event(dev);
> +}
> +
>  static void intel_dp_modeset_retry_work_fn(struct work_struct *work)
>  {
>  	struct intel_dp *intel_dp = container_of(work, typeof(*intel_dp),
>  						 modeset_retry_work);
> -	struct drm_connector *connector = &intel_dp->attached_connector->base;
> +	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> +	struct drm_device *dev = intel_dig_port->base.base.dev;
> +	struct drm_connector *connector;
>  
> -	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n", connector->base.id,
> -		      connector->name);
> +	mutex_lock(&dev->mode_config.mutex);
>  
> -	/* Grab the locks before changing connector property*/
> -	mutex_lock(&connector->dev->mode_config.mutex);
> -	/* Set connector link status to BAD and send a Uevent to notify
> -	 * userspace to do a modeset.
> +	/* Set the connector link status of all (possibly downstream) ports to
> +	 * BAD and send a Uevent to notify userspace to do a modeset.
>  	 */
> -	drm_mode_connector_set_link_status_property(connector,
> -						    DRM_MODE_LINK_STATUS_BAD);
> -	mutex_unlock(&connector->dev->mode_config.mutex);
> +	if (intel_dp->is_mst) {
> +		drm_dp_mst_topology_mgr_lower_link_rate(
> +		    &intel_dp->mst_mgr,
> +		    intel_dp_max_link_rate(intel_dp),
> +		    intel_dp_max_lane_count(intel_dp));
> +	} else {
> +		connector = &intel_dp->attached_connector->base;
> +
> +		DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n",
> +			      connector->base.id, connector->name);
> +		drm_mode_connector_set_link_status_property(
> +		    connector, DRM_MODE_LINK_STATUS_BAD);
> +	}
> +
> +	mutex_unlock(&dev->mode_config.mutex);
> +
>  	/* Send Hotplug uevent so userspace can reprobe */
> -	drm_kms_helper_hotplug_event(connector->dev);
> +	drm_kms_helper_hotplug_event(dev);
>  }
>  
>  bool
> @@ -6302,6 +6477,9 @@ intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
>  	/* Initialize the work for modeset in case of link train failure */
>  	INIT_WORK(&intel_dp->modeset_retry_work,
>  		  intel_dp_modeset_retry_work_fn);
> +	INIT_WORK(&intel_dp->mst_retrain_work,
> +		  intel_dp_mst_retrain_link_work);
> +	init_completion(&intel_dp->mst_retrain_completion);
>  
>  	if (WARN(intel_dig_port->max_lanes < 1,
>  		 "Not enough lanes (%d) for DP on port %c\n",
> diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
> index c0553456b18e..31202f838e89 100644
> --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> @@ -110,21 +110,32 @@ static int intel_dp_mst_atomic_check(struct drm_connector *connector,
>  	struct drm_connector_state *old_conn_state;
>  	struct drm_crtc *old_crtc;
>  	struct drm_crtc_state *crtc_state;
> +	struct drm_dp_mst_topology_mgr *mgr;
> +	struct drm_encoder *encoder;
>  	int slots, ret = 0;
> +	bool could_retrain = false;
> +
> +	if (new_conn_state->crtc) {
> +		crtc_state = drm_atomic_get_new_crtc_state(
> +		    state, new_conn_state->crtc);
> +		if (crtc_state && drm_atomic_crtc_needs_modeset(crtc_state))
> +			could_retrain = true;
> +	}
>  
>  	old_conn_state = drm_atomic_get_old_connector_state(state, connector);
>  	old_crtc = old_conn_state->crtc;
>  	if (!old_crtc)
> -		return ret;
> +		goto out;
>  
>  	crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
> -	slots = to_intel_crtc_state(crtc_state)->dp_m_n.tu;
> -	if (drm_atomic_crtc_needs_modeset(crtc_state) && slots > 0) {
> -		struct drm_dp_mst_topology_mgr *mgr;
> -		struct drm_encoder *old_encoder;
> +	if (!drm_atomic_crtc_needs_modeset(crtc_state))
> +		goto out;
> +	could_retrain = true;
>  
> -		old_encoder = old_conn_state->best_encoder;
> -		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
> +	slots = to_intel_crtc_state(crtc_state)->dp_m_n.tu;
> +	if (slots > 0) {
> +		encoder = old_conn_state->best_encoder;
> +		mgr = &enc_to_mst(encoder)->primary->dp.mst_mgr;
>  
>  		ret = drm_dp_atomic_release_vcpi_slots(state, mgr, slots);
>  		if (ret)
> @@ -132,6 +143,18 @@ static int intel_dp_mst_atomic_check(struct drm_connector *connector,
>  		else
>  			to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
>  	}
> +
> +out:
> +	if (could_retrain &&
> +	    old_conn_state->link_status == DRM_MODE_LINK_STATUS_BAD) {
> +		if (new_conn_state->best_encoder)
> +			encoder = new_conn_state->best_encoder;
> +		else
> +			encoder = old_conn_state->best_encoder;
> +
> +		mgr = &enc_to_mst(encoder)->primary->dp.mst_mgr;
> +		ret = drm_atomic_dp_mst_retrain_topology(state, mgr);
> +	}
>  	return ret;
>  }
>  
> @@ -186,9 +209,12 @@ static void intel_mst_post_disable_dp(struct intel_encoder *encoder,
>  	intel_dp->active_mst_links--;
>  
>  	intel_mst->connector = NULL;
> -	if (intel_dp->active_mst_links == 0)
> +	if (intel_dp->active_mst_links == 0) {
> +		intel_dp->mst_link_is_bad = false;
> +
>  		intel_dig_port->base.post_disable(&intel_dig_port->base,
>  						  old_crtc_state, NULL);
> +	}
>  
>  	DRM_DEBUG_KMS("active links %d\n", intel_dp->active_mst_links);
>  }
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index fc338529e918..f4a5861e4dff 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -1119,6 +1119,13 @@ struct intel_dp {
>  	/* mst connector list */
>  	struct intel_dp_mst_encoder *mst_encoders[I915_MAX_PIPES];
>  	struct drm_dp_mst_topology_mgr mst_mgr;
> +	/* We can't handle retraining from the dig workqueue, so... */
> +	struct work_struct mst_retrain_work;
> +	struct completion mst_retrain_completion;
> +	/* Set when retraining the link at the current parameters is
> +	 * impossible for an MST connection
> +	 */
> +	bool mst_link_is_bad;
>  
>  	uint32_t (*get_aux_clock_divider)(struct intel_dp *dp, int index);
>  	/*
> @@ -1686,6 +1693,7 @@ void intel_dp_compute_rate(struct intel_dp *intel_dp, int port_clock,
>  bool intel_dp_source_supports_hbr2(struct intel_dp *intel_dp);
>  bool
>  intel_dp_get_link_status(struct intel_dp *intel_dp, uint8_t link_status[DP_LINK_STATUS_SIZE]);
> +int intel_dp_get_crtc_mask(struct intel_dp *intel_dp);
>  
>  static inline unsigned int intel_dp_unused_lane_mask(int lane_count)
>  {
> -- 
> 2.14.3
> 
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