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 <ly...@redhat.com>
> Cc: Manasi Navare <manasi.d.nav...@intel.com>
> Cc: Ville Syrjälä <ville.syrj...@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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