drm/i915/lvds: Always use the presence pin for LVDS on PCH

With the introduction of the PCH, we gained an LVDS presence pin but we
continued to use the existing logic that asserted that LVDS was only
supported on certain mobile chipsets. However, there are desktop
IronLake systems with LVDS attached which we fail to detect. So for PCH,
trust the LVDS presence pin and quirk all the lying manufacturers.

Tested-by: Daniel Woff <wolff.daniel@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=43171
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -7755,10 +7755,9 @@ static void intel_setup_outputs(struct drm_device *dev)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_encoder *encoder;
 	bool dpd_is_edp = false;
-	bool has_lvds = false;
+	bool has_lvds;
 
-	if (IS_MOBILE(dev) && !IS_I830(dev))
-		has_lvds = intel_lvds_init(dev);
+	has_lvds = intel_lvds_init(dev);
 	if (!has_lvds && !HAS_PCH_SPLIT(dev)) {
 		/* disable the panel fitter on everything but LVDS */
 		I915_WRITE(PFIT_CONTROL, 0);

drivers/gpu/drm/i915/intel_lvds.c

@@ -844,6 +844,18 @@ static bool lvds_is_present_in_vbt(struct drm_device *dev,
 	return false;
 }
 
+static bool intel_lvds_supported(struct drm_device *dev)
+{
+	/* With the introduction of the PCH we gained a dedicated
+	 * LVDS presence pin, use it. */
+	if (HAS_PCH_SPLIT(dev))
+		return true;
+
+	/* Otherwise LVDS was only attached to mobile products,
+	 * except for the inglorious 830gm */
+	return IS_MOBILE(dev) && !IS_I830(dev);
+}
+
 /**
  * intel_lvds_init - setup LVDS connectors on this device
  * @dev: drm device
@@ -865,6 +877,9 @@ bool intel_lvds_init(struct drm_device *dev)
 	int pipe;
 	u8 pin;
 
+	if (!intel_lvds_supported(dev))
+		return false;
+
 	/* Skip init on machines we know falsely report LVDS */
 	if (dmi_check_system(intel_no_lvds))
 		return false;