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 56071a207602a451f0c46d3dcc8379b59ef576e2
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=81647
Tested-by: Adam Jirasek <libm3l@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=79386
Tested-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>

1 files changed, 9 insertions, 17 deletions

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index ab7cd0a75bd5..72bf533596c8 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/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. */
-                        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]);
-                }
+                /*
+                 * 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;
+                min_clock = max_clock;
         }
 
         for (; bpp >= 6*3; bpp -= 2*3) {