drm/bridge: Add the drm_for_each_bridge_in_chain() helper

To iterate over all bridges attached to a specific encoder.
Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191203141515.3597631-6-boris.brezillon@collabora.com

include/drm/drm_bridge.h

@@ -441,6 +441,17 @@ drm_bridge_chain_get_first_bridge(struct drm_encoder *encoder)
 					struct drm_bridge, chain_node);
 }
 
+/**
+ * drm_for_each_bridge_in_chain() - Iterate over all bridges present in a chain
+ * @encoder: the encoder to iterate bridges on
+ * @bridge: a bridge pointer updated to point to the current bridge at each
+ *	    iteration
+ *
+ * Iterate over all bridges present in the bridge chain attached to @encoder.
+ */
+#define drm_for_each_bridge_in_chain(encoder, bridge)			\
+	list_for_each_entry(bridge, &(encoder)->bridge_chain, chain_node)
+
 bool drm_bridge_chain_mode_fixup(struct drm_bridge *bridge,
 				 const struct drm_display_mode *mode,
 				 struct drm_display_mode *adjusted_mode);