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Commit 425904dd authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915: Addin-offset is an unreliable indicator of LVDS presence (v2) 



My Samsung N210 has a VBT with DEVICE_TYPE_INT_LFP with a zero
addin-offset. With the check in place, the panel was declared absent.

v2: Only trust BIOS writers that have graduated to writing OpRegions.
(We are all doomed.)

Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: Zhao Yakui <yakui.zhao@intel.com>
Cc: Adam Jackson <ajax@redhat.com>
Reviewed-by: default avatarAdam Jackson <ajax@redhat.com>
parent 44834a67

drivers/gpu/drm/i915/intel_lvds.c

+26 −20
Original line number Diff line number Diff line
@@ -777,38 +777,44 @@ static void intel_find_lvds_downclock(struct drm_device *dev, 
 * If it is present, return 1.

 * If it is not present, return false.

 * If no child dev is parsed from VBT, it assumes that the LVDS is present.

 * Note: The addin_offset should also be checked for LVDS panel.

 * Only when it is non-zero, it is assumed that it is present.

 */

static int lvds_is_present_in_vbt(struct drm_device *dev)

static bool lvds_is_present_in_vbt(struct drm_device *dev)

{

	struct drm_i915_private *dev_priv = dev->dev_private;

	struct child_device_config *p_child;

	int i, ret;

	int i;



	if (!dev_priv->child_dev_num)

		return 1;

		return true;



	ret = 0;

	for (i = 0; i < dev_priv->child_dev_num; i++) {

		p_child = dev_priv->child_dev + i;

		/*

		 * If the device type is not LFP, continue.

		 * If the device type is 0x22, it is also regarded as LFP.

		struct child_device_config *child = dev_priv->child_dev + i;



		/* If the device type is not LFP, continue.

		 * We have to check both the new identifiers as well as the

		 * old for compatibility with some BIOSes.

		 */

		if (p_child->device_type != DEVICE_TYPE_INT_LFP &&

			p_child->device_type != DEVICE_TYPE_LFP)

		if (child->device_type != DEVICE_TYPE_INT_LFP &&

		    child->device_type != DEVICE_TYPE_LFP)

			continue;



		/* The addin_offset should be checked. Only when it is

		 * non-zero, it is regarded as present.

		/* However, we cannot trust the BIOS writers to populate

		 * the VBT correctly.  Since LVDS requires additional

		 * information from AIM blocks, a non-zero addin offset is

		 * a good indicator that the LVDS is actually present.

		 */

		if (p_child->addin_offset) {

			ret = 1;

			break;

		}

		if (child->addin_offset)

			return true;



		/* But even then some BIOS writers perform some black magic

		 * and instantiate the device without reference to any

		 * additional data.  Trust that if the VBT was written into

		 * the OpRegion then they have validated the LVDS's existence.

		 */

		if (dev_priv->opregion.vbt)

			return true;

	}

	return ret;



	return false;

}



/**