drm/i915/dp: Link train Fallback on eDP only if fallback link BW can fit panel's...

This patch fixes the original commit c0cfb10d9e1de49 ("drm/i915/edp:
Do not do link training fallback or prune modes on EDP") that causes
a blank screen in case of certain eDP panels (Eg: seen on Dell XPS13 9350)
where first link training fails and a retraining is required by falling
back to lower link rate/lane count.
In case of some panels they advertise higher link rate/lane count
than whats required for supporting the panel's native mode.
But we always link train at highest link rate/lane count for eDP
and if that fails we can still fallback to lower link rate/lane count
as long as the fallback link BW still fits the native mode to avoid
pruning the panel's native mode yet retraining at fallback values
to recover from a blank screen.

v3:
* Add const for fixed_mode (Ville)
v2:
* Send uevent if link failure on eDP unconditionally

Fixes: c0cfb10d9e1d ("drm/i915/edp: Do not do link training fallback or prune modes on EDP")
Cc: Clinton Taylor <clinton.a.taylor@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: <stable@vger.kernel.org> # v4.17+
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107489
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105338
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Tested-by: Alexander Wilson <alexander.wilson@ncf.edu>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181009212804.702-1-manasi.d.navare@intel.com

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 0855b9785f7b23ce4b3700b3c8350ad0d900b97e..13ff89be6ad6a2626eaf6392a476296e06d4f406 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -557,6 +557,22 @@ static bool intel_dp_link_params_valid(struct intel_dp *intel_dp, int link_rate,
        return true;
 }
 
+static bool intel_dp_can_link_train_fallback_for_edp(struct intel_dp *intel_dp,
+                                                    int link_rate,
+                                                    uint8_t lane_count)
+{
+       const struct drm_display_mode *fixed_mode =
+               intel_dp->attached_connector->panel.fixed_mode;
+       int mode_rate, max_rate;
+
+       mode_rate = intel_dp_link_required(fixed_mode->clock, 18);
+       max_rate = intel_dp_max_data_rate(link_rate, lane_count);
+       if (mode_rate > max_rate)
+               return false;
+
+       return true;
+}
+
 int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
                                            int link_rate, uint8_t lane_count)
 {
@@ -566,9 +582,23 @@ int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
                                    intel_dp->num_common_rates,
                                    link_rate);
        if (index > 0) {
+               if (intel_dp_is_edp(intel_dp) &&
+                   !intel_dp_can_link_train_fallback_for_edp(intel_dp,
+                                                             intel_dp->common_rates[index - 1],
+                                                             lane_count)) {
+                       DRM_DEBUG_KMS("Retrying Link training for eDP with same parameters\n");
+                       return 0;
+               }
                intel_dp->max_link_rate = intel_dp->common_rates[index - 1];
                intel_dp->max_link_lane_count = lane_count;
        } else if (lane_count > 1) {
+               if (intel_dp_is_edp(intel_dp) &&
+                   !intel_dp_can_link_train_fallback_for_edp(intel_dp,
+                                                             intel_dp_max_common_rate(intel_dp),
+                                                             lane_count >> 1)) {
+                       DRM_DEBUG_KMS("Retrying Link training for eDP with same parameters\n");
+                       return 0;
+               }
                intel_dp->max_link_rate = intel_dp_max_common_rate(intel_dp);
                intel_dp->max_link_lane_count = lane_count >> 1;
        } else {

diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
index a9f40985a621209a4d192059eb0474a19748e206..30be0e39bd5fda1afd705f44f840260d6177abbf 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -367,22 +367,14 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
        return;
 
  failure_handling:
-       /* Dont fallback and prune modes if its eDP */
-       if (!intel_dp_is_edp(intel_dp)) {
-               DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
-                             intel_connector->base.base.id,
-                             intel_connector->base.name,
-                             intel_dp->link_rate, intel_dp->lane_count);
-               if (!intel_dp_get_link_train_fallback_values(intel_dp,
-                                                            intel_dp->link_rate,
-                                                            intel_dp->lane_count))
-                       /* Schedule a Hotplug Uevent to userspace to start modeset */
-                       schedule_work(&intel_connector->modeset_retry_work);
-       } else {
-               DRM_ERROR("[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
-                         intel_connector->base.base.id,
-                         intel_connector->base.name,
-                         intel_dp->link_rate, intel_dp->lane_count);
-       }
+       DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
+                     intel_connector->base.base.id,
+                     intel_connector->base.name,
+                     intel_dp->link_rate, intel_dp->lane_count);
+       if (!intel_dp_get_link_train_fallback_values(intel_dp,
+                                                    intel_dp->link_rate,
+                                                    intel_dp->lane_count))
+               /* Schedule a Hotplug Uevent to userspace to start modeset */
+               schedule_work(&intel_connector->modeset_retry_work);
        return;
 }