[PATCH] drm/i915/dp: Link train Fallback on eDP only if fallback link BW can fit panel's native mode

* [PATCH] drm/i915/dp: Link train Fallback on eDP only if fallback link BW can fit panel's native mode
@ 2018-05-17  2:21 Manasi Navare
  2018-05-17  2:45 ` ✗ Fi.CI.CHECKPATCH: warning for " Patchwork
                   ` (4 more replies)
  0 siblings, 5 replies; 12+ messages in thread
From: Manasi Navare @ 2018-05-17  2:21 UTC (permalink / raw)
  To: intel-gfx; +Cc: Daniel Vetter, Lucas De Marchi

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.

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>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c               | 25 +++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_dp_link_training.c | 26 +++++++++-----------------
 2 files changed, 34 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 2cc58596..7f7202a 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -387,6 +387,21 @@ 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)
+{
+	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)
 {
@@ -396,9 +411,19 @@ 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))
+			return -1;
 		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))
+			return -1;
 		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 3fcaa98..6673975 100644
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -335,22 +335,14 @@ 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;
 }
-- 
2.7.4

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