drm/i915: do not default to 18 bpp for eDP if missing from VBT

commit 500a8cc4
Author: Zhenyu Wang <zhenyuw@linux.intel.com>
Date:   Wed Jan 13 11:19:52 2010 +0800

    drm/i915: parse eDP panel color depth from VBT block

originally introduced parsing bpp for eDP from VBT, with a default of 18
bpp if the eDP BIOS data block is not present. Turns out that default seems
to break the Macbook Pro with retina display, as noted in

commit 4344b813
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Fri Aug 10 11:10:20 2012 +0200

    drm/i915: ignore eDP bpc settings from vbt

Since we can't ignore bpc settings from VBT completely after all, get rid
of the default. Do not clamp eDP to 18 bpp by default if the eDP BDB is
missing from VBT.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Tested-by: NHenrik Rydberg <rydberg@euromail.se>
[danvet: paste in the updated commit message from irc.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_bios.c

@@ -499,12 +499,8 @@ parse_edp(struct drm_i915_private *dev_priv, struct bdb_header *bdb)
 
 	edp = find_section(bdb, BDB_EDP);
 	if (!edp) {
-		if (SUPPORTS_EDP(dev_priv->dev) && dev_priv->edp.support) {
-			DRM_DEBUG_KMS("No eDP BDB found but eDP panel "
-				      "supported, assume %dbpp panel color "
-				      "depth.\n",
-				      dev_priv->edp.bpp);
-		}
+		if (SUPPORTS_EDP(dev_priv->dev) && dev_priv->edp.support)
+			DRM_DEBUG_KMS("No eDP BDB found but eDP panel supported.\n");
 		return;
 	}
 
@@ -657,9 +653,6 @@ init_vbt_defaults(struct drm_i915_private *dev_priv)
 	dev_priv->lvds_use_ssc = 1;
 	dev_priv->lvds_ssc_freq = intel_bios_ssc_frequency(dev, 1);
 	DRM_DEBUG_KMS("Set default to SSC at %dMHz\n", dev_priv->lvds_ssc_freq);
-
-	/* eDP data */
-	dev_priv->edp.bpp = 18;
 }
 
 static int __init intel_no_opregion_vbt_callback(const struct dmi_system_id *id)

drivers/gpu/drm/i915/intel_display.c

@@ -3845,7 +3845,7 @@ static bool intel_choose_pipe_bpp_dither(struct drm_crtc *crtc,
 			/* Use VBT settings if we have an eDP panel */
 			unsigned int edp_bpc = dev_priv->edp.bpp / 3;
 
-			if (edp_bpc < display_bpc) {
+			if (edp_bpc && edp_bpc < display_bpc) {
 				DRM_DEBUG_KMS("clamping display bpc (was %d) to eDP (%d)\n", display_bpc, edp_bpc);
 				display_bpc = edp_bpc;
 			}