3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jani Nikula <redacted>

commit 9a30a61f3516871c5c638fd7c025fbaa11ddf7fe upstream.

commit 500a8cc466a24e2fbc4c86ef9c6467ae2ffdeb0c
Author: Zhenyu Wang [off-list ref]
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 4344b813f105a19f793f1fd93ad775b784648b95
Author: Daniel Vetter [off-list ref]
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: Jani Nikula <redacted>
Tested-by: Henrik Rydberg <redacted>
[danvet: paste in the updated commit message from irc.]
Signed-off-by: Daniel Vetter <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/i915/intel_bios.c    |   11 ++---------
 drivers/gpu/drm/i915/intel_display.c |    2 +-
 2 files changed, 3 insertions(+), 10 deletions(-)

--- a/drivers/gpu/drm/i915/intel_bios.c
+++ b/drivers/gpu/drm/i915/intel_bios.c

@@ -459,12 +459,8 @@ parse_edp(struct drm_i915_private *dev_p
 
 	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;
 	}
 

@@ -617,9 +613,6 @@ init_vbt_defaults(struct drm_i915_privat
 	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)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c

@@ -5000,7 +5000,7 @@ static bool intel_choose_pipe_bpp_dither
 			/* 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;
 			}