[Intel-gfx] [PATCH v2 4/4] drm/i915/dp: Check eDP fallback link BW against downclock mode

[Manasi Navare]

If link training fails on eDP then we fallback to lower link rate
and lane count. If the fallback link BW cannot fit the panel's native
mode and if the downclock mode exists then we should check if the fallback
BW can fit this downclock mode.

Suggested-by: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 0e400629e85c..bfc56e778d0f 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -562,12 +562,21 @@ static bool intel_dp_can_link_train_fallback_for_edp(struct intel_dp *intel_dp,
 						     uint8_t lane_count)
 {
 	struct drm_display_mode *fixed_mode = intel_dp->attached_connector->panel.fixed_mode;
+	struct drm_display_mode *downclock_mode =
+		intel_dp->attached_connector->panel.downclock_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)
+	if (mode_rate > max_rate) {
+		if (downclock_mode) {
+			mode_rate = intel_dp_link_required(downclock_mode->clock,
+							   18);
+			if (mode_rate > max_rate)
+				return false;
+		}
 		return false;
+	}
 
 	return true;
 }
-- 
2.18.0