[PATCH] drm/i915: prefer VBT modes for SVDO-LVDS over EDID

[Daniel Vetter <daniel.vetter@ffwll.ch>]

In

commit 53d3b4d7778daf15900867336c85d3f8dd70600c
Author: Egbert Eich <eich@suse.de>
Date:   Tue Jun 4 17:13:21 2013 +0200

    drm/i915/sdvo: Use &intel_sdvo->ddc instead of intel_sdvo->i2c for DDC

Ebgert Eich fixed a long-standing bug where we simply used a
non-working i2c controller to read the EDID for SDVO-LVDS panels.
Unfortunately some machines seem to not be able to cope with the mode
provided in the EDID (specifically they seem to not be able to cope
with a 4x pixel mutliplier instead of a 2x one).

Since it took forever to notice the breakage it's fairly safe to
assume that at least for SDVO-LVDS panels the VBT contains fairly sane
data. So just switch around the order and use VBT modes first.

Cc: Egbert Eich <eich@suse.de>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=65524
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_sdvo.c |   23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_sdvo.c b/drivers/gpu/drm/i915/intel_sdvo.c
index 4c47b44..da3da8d 100644
--- a/drivers/gpu/drm/i915/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/intel_sdvo.c
@@ -1771,17 +1771,9 @@ static void intel_sdvo_get_lvds_modes(struct drm_connector *connector)
 	struct drm_i915_private *dev_priv = connector->dev->dev_private;
 	struct drm_display_mode *newmode;
 
-	/*
-	 * Attempt to get the mode list from DDC.
-	 * Assume that the preferred modes are
-	 * arranged in priority order.
-	 */
-	intel_ddc_get_modes(connector, &intel_sdvo->ddc);
-	if (list_empty(&connector->probed_modes) == false)
-		goto end;
-
-	/* Fetch modes from VBT */
-	if (dev_priv->sdvo_lvds_vbt_mode != NULL) {
+	/* Fetch modes from VBT. For SDVO prefer the VBT mode since some
+	 * SDVO->LVDS transcoders can't cope with the EDID mode. */
+	if (dev_priv->vbt.sdvo_lvds_vbt_mode != NULL) {
 		newmode = drm_mode_duplicate(connector->dev,
 					     dev_priv->sdvo_lvds_vbt_mode);
 		if (newmode != NULL) {
@@ -1789,9 +1781,18 @@ static void intel_sdvo_get_lvds_modes(struct drm_connector *connector)
 			newmode->type = (DRM_MODE_TYPE_PREFERRED |
 					 DRM_MODE_TYPE_DRIVER);
 			drm_mode_probed_add(connector, newmode);
+
+			goto end;
 		}
 	}
 
+	/*
+	 * Attempt to get the mode list from DDC.
+	 * Assume that the preferred modes are
+	 * arranged in priority order.
+	 */
+	intel_ddc_get_modes(connector, &intel_sdvo->ddc);
+
 end:
 	list_for_each_entry(newmode, &connector->probed_modes, head) {
 		if (newmode->type & DRM_MODE_TYPE_PREFERRED) {
-- 
1.7.10.4