drm/atomic: add plane iterator macros

Add helper macros to iterate the current, or incoming set of planes
attached to a crtc.  These helpers are only available for drivers
converted to use atomic-helpers.

Signed-off-by: Rob Clark <robdclark@gmail.com>
[danvet: Squash in fixup from Rob to move the planemask iterator to
drm_crtc.h and document it. That one is needed by the atomic ioctl so
can't be in a helper library.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 4cf6905..dd2c16e 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1062,6 +1062,19 @@
 	uint32_t cursor_width, cursor_height;
 };
 
+/**
+ * drm_for_each_plane_mask - iterate over planes specified by bitmask
+ * @plane: the loop cursor
+ * @dev: the DRM device
+ * @plane_mask: bitmask of plane indices
+ *
+ * Iterate over all planes specified by bitmask.
+ */
+#define drm_for_each_plane_mask(plane, dev, plane_mask) \
+	list_for_each_entry((plane), &(dev)->mode_config.plane_list, head) \
+		if ((plane_mask) & (1 << drm_plane_index(plane)))
+
+
 #define obj_to_crtc(x) container_of(x, struct drm_crtc, base)
 #define obj_to_connector(x) container_of(x, struct drm_connector, base)
 #define obj_to_encoder(x) container_of(x, struct drm_encoder, base)