drm/i915: Ignore LVDS EDID when it is unavailabe or invalid

This trys to shut up complains about invalid LVDS EDID during
mode probe, but uses fixed panel mode directly for panels with
broken EDID.

https://bugs.freedesktop.org/show_bug.cgi?id=23099
https://bugs.freedesktop.org/show_bug.cgi?id=26395

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Tested-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_drv.h

@@ -611,6 +611,8 @@ typedef struct drm_i915_private {
 	/* Reclocking support */
 	bool render_reclock_avail;
 	bool lvds_downclock_avail;
+	/* indicate whether the LVDS EDID is OK */
+	bool lvds_edid_good;
 	/* indicates the reduced downclock for LVDS*/
 	int lvds_downclock;
 	struct work_struct idle_work;

drivers/gpu/drm/i915/intel_lvds.c

@@ -638,10 +638,12 @@ static int intel_lvds_get_modes(struct drm_connector *connector)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	int ret = 0;
 
-	ret = intel_ddc_get_modes(intel_encoder);
+	if (dev_priv->lvds_edid_good) {
+		ret = intel_ddc_get_modes(intel_encoder);
 
-	if (ret)
-		return ret;
+		if (ret)
+			return ret;
+	}
 
 	/* Didn't get an EDID, so
 	 * Set wide sync ranges so we get all modes
@@ -1062,7 +1064,10 @@ void intel_lvds_init(struct drm_device *dev)
 	 * Attempt to get the fixed panel mode from DDC.  Assume that the
 	 * preferred mode is the right one.
 	 */
-	intel_ddc_get_modes(intel_encoder);
+	dev_priv->lvds_edid_good = true;
+
+	if (!intel_ddc_get_modes(intel_encoder))
+		dev_priv->lvds_edid_good = false;
 
 	list_for_each_entry(scan, &connector->probed_modes, head) {
 		mutex_lock(&dev->mode_config.mutex);