drm/i915: Replicate BIOS eDP bpp clamping hack for hsw

Haswell's DDI encoders have their own ->get_config callback and in

commit c6cd2ee2
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Mon Oct 21 10:52:07 2013 +0300

    drm/i915/dp: workaround BIOS eDP bpp clamping issue

we've forgotten to replicate this hack. So let's do it that.

Note for backporters: The above commit and all it's depencies need to
be backported first.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=71049
Cc: stable@vger.kernel.org
Tested-by: Gökçen Eraslan <gokcen.eraslan@gmail.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -1406,6 +1406,26 @@ void intel_ddi_get_config(struct intel_encoder *encoder,
 	default:
 		break;
 	}
+
+	if (encoder->type == INTEL_OUTPUT_EDP && dev_priv->vbt.edp_bpp &&
+	    pipe_config->pipe_bpp > dev_priv->vbt.edp_bpp) {
+		/*
+		 * This is a big fat ugly hack.
+		 *
+		 * Some machines in UEFI boot mode provide us a VBT that has 18
+		 * bpp and 1.62 GHz link bandwidth for eDP, which for reasons
+		 * unknown we fail to light up. Yet the same BIOS boots up with
+		 * 24 bpp and 2.7 GHz link. Use the same bpp as the BIOS uses as
+		 * max, not what it tells us to use.
+		 *
+		 * Note: This will still be broken if the eDP panel is not lit
+		 * up by the BIOS, and thus we can't get the mode at module
+		 * load.
+		 */
+		DRM_DEBUG_KMS("pipe has %d bpp for eDP panel, overriding BIOS-provided max %d bpp\n",
+			      pipe_config->pipe_bpp, dev_priv->vbt.edp_bpp);
+		dev_priv->vbt.edp_bpp = pipe_config->pipe_bpp;
+	}
 }
 
 static void intel_ddi_destroy(struct drm_encoder *encoder)