drm/i915/dp: fall back to 18 bpp when sink capability is unknown

Per DP spec, the source device should fall back to 18 bpp, VESA range
RGB when the sink capability is unknown. Fix the color depth
clamping. 18 bpp color depth should ensure full color range in automatic
mode.

The clamping has been HDMI specific since its introduction in

commit 996a2239f93b03c5972923f04b097f65565c5bed
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Fri Apr 19 11:24:34 2013 +0200

    drm/i915: Disable high-bpc on pre-1.4 EDID screens

Cc: stable@vger.kernel.org
Reported-and-tested-by: Dihan Wickremasuriya <nayomal@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=105331
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452695720-7076-1-git-send-email-jani.nikula@intel.com
(cherry picked from commit 013dd9e038723bbd2aa67be51847384b75be8253)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 2f00828ccc6e923a65447424c716d9cc5ee0e99b..002ce89de412da43713e437aaa8597c11e5f309b 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12075,11 +12075,21 @@ connected_sink_compute_bpp(struct intel_connector *connector,
                pipe_config->pipe_bpp = connector->base.display_info.bpc*3;
        }
 
-       /* Clamp bpp to 8 on screens without EDID 1.4 */
-       if (connector->base.display_info.bpc == 0 && bpp > 24) {
-               DRM_DEBUG_KMS("clamping display bpp (was %d) to default limit of 24\n",
-                             bpp);
-               pipe_config->pipe_bpp = 24;
+       /* Clamp bpp to default limit on screens without EDID 1.4 */
+       if (connector->base.display_info.bpc == 0) {
+               int type = connector->base.connector_type;
+               int clamp_bpp = 24;
+
+               /* Fall back to 18 bpp when DP sink capability is unknown. */
+               if (type == DRM_MODE_CONNECTOR_DisplayPort ||
+                   type == DRM_MODE_CONNECTOR_eDP)
+                       clamp_bpp = 18;
+
+               if (bpp > clamp_bpp) {
+                       DRM_DEBUG_KMS("clamping display bpp (was %d) to default limit of %d\n",
+                                     bpp, clamp_bpp);
+                       pipe_config->pipe_bpp = clamp_bpp;
+               }
        }
 }