drm/i915: Use ACPI OpRegion to determine lid status

Admittedly, trusting ACPI or the BIOS at all to be correct is littered
with numerous examples where it is wrong. Maybe, just maybe, we will
have better luck using the ACPI OpRegion lid status...
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_drv.h

@@ -111,6 +111,7 @@ struct intel_opregion {
 	struct opregion_swsci *swsci;
 	struct opregion_asle *asle;
 	void *vbt;
+	u32 __iomem *lid_state;
 };
 #define OPREGION_SIZE            (8*1024)
 

drivers/gpu/drm/i915/intel_lvds.c

@@ -472,8 +472,15 @@ static enum drm_connector_status
 intel_lvds_detect(struct drm_connector *connector, bool force)
 {
 	struct drm_device *dev = connector->dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
 	enum drm_connector_status status = connector_status_connected;
 
+	/* Assume that the BIOS does not lie through the OpRegion... */
+	if (dev_priv->opregion.lid_state)
+		return ioread32(dev_priv->opregion.lid_state) & 0x1 ?
+			connector_status_connected :
+			connector_status_disconnected;
+
 	/* ACPI lid methods were generally unreliable in this generation, so
 	 * don't even bother.
 	 */

drivers/gpu/drm/i915/intel_opregion.c

@@ -488,6 +488,8 @@ int intel_opregion_setup(struct drm_device *dev)
 	opregion->header = base;
 	opregion->vbt = base + OPREGION_VBT_OFFSET;
 
+	opregion->lid_state = base + 0x01ac;
+
 	mboxes = opregion->header->mboxes;
 	if (mboxes & MBOX_ACPI) {
 		DRM_DEBUG_DRIVER("Public ACPI methods supported\n");