drm/i915/edp: use lane count and link rate from DPCD for eDP

eDP panels are generally designed to support only a single clock and
lane configuration.

commit 56071a20
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Tue May 6 14:56:52 2014 +0300

    drm/i915: use lane count and link rate from VBT as minimums for eDP

should have started using the optimal link parameters for eDP
panels. Turns out a certain other OS uses DPCD instead of VBT, which
means trusting VBT on this may not be so reliable after all. Follow
suit.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=81647Tested-by: Adam Jirasek <libm3l@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=79386Tested-by: Narthana Epa <narthana.epa+freedesktop@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dp.c

@@ -1068,23 +1068,15 @@ intel_dp_compute_config(struct intel_encoder *encoder,
 			bpp = dev_priv->vbt.edp_bpp;
 		}
 
-		if (IS_BROADWELL(dev)) {
-			/* Yes, it's an ugly hack. */
+		/*
+		 * Use the maximum clock and number of lanes the eDP panel
+		 * advertizes being capable of. The panels are generally
+		 * designed to support only a single clock and lane
+		 * configuration, and typically these values correspond to the
+		 * native resolution of the panel.
+		 */
 		min_lane_count = max_lane_count;
-			DRM_DEBUG_KMS("forcing lane count to max (%u) on BDW\n",
-				      min_lane_count);
-		} else if (dev_priv->vbt.edp_lanes) {
-			min_lane_count = min(dev_priv->vbt.edp_lanes,
-					     max_lane_count);
-			DRM_DEBUG_KMS("using min %u lanes per VBT\n",
-				      min_lane_count);
-		}
-
-		if (dev_priv->vbt.edp_rate) {
-			min_clock = min(dev_priv->vbt.edp_rate >> 3, max_clock);
-			DRM_DEBUG_KMS("using min %02x link bw per VBT\n",
-				      bws[min_clock]);
-		}
+		min_clock = max_clock;
 	}
 
 	for (; bpp >= 6*3; bpp -= 2*3) {