[RFC PATCH 4/5] drm/i915: make intel_lvds_get_edid() more robust

[Seth Forshee <seth.forshee@canonical.com>]

intel_lvds_get_edid() needs to be called when switching GPUs, but it's
currently making assumptions that it will only be called once and that
there's always an LVDS connector present when it's called. Fix these
assumptions.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 drivers/gpu/drm/i915/intel_lvds.c |   17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_lvds.c b/drivers/gpu/drm/i915/intel_lvds.c
index c1ab632..9d05a90 100644
--- a/drivers/gpu/drm/i915/intel_lvds.c
+++ b/drivers/gpu/drm/i915/intel_lvds.c
@@ -906,9 +906,18 @@ static bool intel_lvds_get_edid(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_connector *connector = dev_priv->int_lvds_connector;
-	struct intel_lvds *intel_lvds = intel_attached_lvds(connector);
+	struct intel_lvds *intel_lvds;
 	struct drm_display_mode *scan; /* *modes, *bios_mode; */
 
+	if (!connector)
+		return false;
+
+	intel_lvds = intel_attached_lvds(connector);
+
+	/* If we already have an EDID, no need to check again */
+	if (intel_lvds->edid)
+		return true;
+
 	/*
 	 * Attempt to get the fixed panel mode from DDC.  Assume that the
 	 * preferred mode is the right one.
@@ -939,6 +948,12 @@ static bool intel_lvds_get_edid(struct drm_device *dev)
 
 	list_for_each_entry(scan, &connector->probed_modes, head) {
 		if (scan->type & DRM_MODE_TYPE_PREFERRED) {
+			/*
+			 * If we already have a preferred mode from another
+			 * source, prefer the one from the EDID.
+			 */
+			if (intel_lvds->fixed_mode)
+				drm_mode_destroy(dev, intel_lvds->fixed_mode);
 			intel_lvds->fixed_mode =
 				drm_mode_duplicate(dev, scan);
 			intel_find_lvds_downclock(dev,
-- 
1.7.9.5