[Bug 81647] [hsw bisected] flickering blurry screen, prefer fast over wide dp link param

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=81647

Jani Nikula <jani.nikula at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |NEEDINFO

--- Comment #5 from Jani Nikula <jani.nikula at intel.com> ---
(In reply to comment #4)
> (In reply to comment #3)
> > Note this is a case where the earlier regression triumphs, and so this bug
> > must persist until the root cause is known (i.e. we can fix this without
> > breaking working machines).
> 
> Is there anything I can do to help?

I presume this is the laptop panel. Please try this patch:

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index d7fc2c0e9ba8..f4248d7f64f9 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -889,23 +889,13 @@ 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. 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) {

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