drm/edid: add function to help find SADs

Add a function to find the start of the SADs in the ELD.  This
complements the helper to retrieve the SAD count.

[airlied: this fixes a build problem with the alsa eld helper
which required this].
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/drm_edid.h

@@ -347,6 +347,25 @@ static inline int drm_eld_mnl(const uint8_t *eld)
 	return (eld[DRM_ELD_CEA_EDID_VER_MNL] & DRM_ELD_MNL_MASK) >> DRM_ELD_MNL_SHIFT;
 }
 
+/**
+ * drm_eld_sad - Get ELD SAD structures.
+ * @eld: pointer to an eld memory structure with sad_count set
+ */
+static inline const uint8_t *drm_eld_sad(const uint8_t *eld)
+{
+	unsigned int ver, mnl;
+
+	ver = (eld[DRM_ELD_VER] & DRM_ELD_VER_MASK) >> DRM_ELD_VER_SHIFT;
+	if (ver != 2 && ver != 31)
+		return NULL;
+
+	mnl = drm_eld_mnl(eld);
+	if (mnl > 16)
+		return NULL;
+
+	return eld + DRM_ELD_CEA_SAD(mnl, 0);
+}
+
 /**
  * drm_eld_sad_count - Get ELD SAD count.
  * @eld: pointer to an eld memory structure with sad_count set