Original patch by Chris Wilson [1], here slightly adapted for the latest tree.

[1] https://bugs.freedesktop.org/attachment.cgi?id=49069


We were checking whether the supplied edid matched the connector it was
read from. We do this in case a DDC read returns an EDID for another
device on a multifunction or otherwise interesting card. However, we
failed to include LVDS as a digital device and so rejecting an otherwise
valid EDID.

Fixes the detection of the secondary SDVO LVDS panel on the Libretto
W105.

diff --git a/drivers/gpu/drm/i915/intel_sdvo.c b/drivers/gpu/drm/i915/intel_sdvo.c
index 3003fb2..ac322fb 100644
--- a/drivers/gpu/drm/i915/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/intel_sdvo.c
@@ -50,6 +50,7 @@
 #define IS_TMDS(c)	(c->output_flag & SDVO_TMDS_MASK)
 #define IS_LVDS(c)	(c->output_flag & SDVO_LVDS_MASK)
 #define IS_TV_OR_LVDS(c) (c->output_flag & (SDVO_TV_MASK | SDVO_LVDS_MASK))
+#define IS_DIGITAL(c) (c->output_flag & (SDVO_TMDS_MASK | SDVO_LVDS_MASK))
 
 
 static const char *tv_format_names[] = {
@@ -1314,6 +1315,18 @@ intel_sdvo_tmds_sink_detect(struct drm_connector *connector)
 	return status;
 }
 
+static bool
+intel_sdvo_connector_matches_edid(struct intel_sdvo_connector *sdvo,
+				struct edid *edid)
+{
+	bool monitor_is_digital = !!(edid->input & DRM_EDID_INPUT_DIGITAL);
+	bool connector_is_digital = !!IS_DIGITAL(sdvo);
+
+	DRM_DEBUG_KMS("connector_is_digital? %d, monitor_is_digital? %d\n",
+			connector_is_digital, monitor_is_digital);
+	return connector_is_digital == monitor_is_digital;
+}
+
 static enum drm_connector_status
 intel_sdvo_detect(struct drm_connector *connector, bool force)
 {
@@ -1358,10 +1371,11 @@ intel_sdvo_detect(struct drm_connector *connector, bool force)
 		if (edid == NULL)
 			edid = intel_sdvo_get_analog_edid(connector);
 		if (edid != NULL) {
-			if (edid->input & DRM_EDID_INPUT_DIGITAL)
-				ret = connector_status_disconnected;
-			else
+			if (intel_sdvo_connector_matches_edid(intel_sdvo_connector,
+								edid))
 				ret = connector_status_connected;
+			else
+				ret = connector_status_disconnected;
 			connector->display_info.raw_edid = NULL;
 			kfree(edid);
 		} else
@@ -1402,11 +1416,8 @@ static void intel_sdvo_get_ddc_modes(struct drm_connector *connector)
 		edid = intel_sdvo_get_analog_edid(connector);
 
 	if (edid != NULL) {
-		struct intel_sdvo_connector *intel_sdvo_connector = to_intel_sdvo_connector(connector);
-		bool monitor_is_digital = !!(edid->input & DRM_EDID_INPUT_DIGITAL);
-		bool connector_is_digital = !!IS_TMDS(intel_sdvo_connector);
-
-		if (connector_is_digital == monitor_is_digital) {
+		if (intel_sdvo_connector_matches_edid(to_intel_sdvo_connector(connector),
+							edid)) {
 			drm_mode_connector_update_edid_property(connector, edid);
 			drm_add_edid_modes(connector, edid);
 		}