drm/bridge: Add a drm_bridge_state object

One of the last remaining objects to not have its atomic state.

This is being motivated by our attempt to support runtime bus-format
negotiation between elements of the bridge chain.
This patch just paves the road for such a feature by adding a new
drm_bridge_state object inheriting from drm_private_obj so we can
re-use some of the existing state initialization/tracking logic.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed by: Jernej Skrabec <jernej.skrabec@siol.net>
Tested-by: Jonas Karlman <jonas@kwiboo.se>
Link: https://patchwork.freedesktop.org/patch/msgid/20200106143409.32321-2-narmstrong@baylibre.com

drivers/gpu/drm/drm_atomic.c

@@ -30,6 +30,7 @@
 
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_uapi.h>
+#include <drm/drm_bridge.h>
 #include <drm/drm_debugfs.h>
 #include <drm/drm_device.h>
 #include <drm/drm_drv.h>
@@ -1017,6 +1018,44 @@ static void drm_atomic_connector_print_state(struct drm_printer *p,
 		connector->funcs->atomic_print_state(p, state);
 }
 
+/**
+ * drm_atomic_add_encoder_bridges - add bridges attached to an encoder
+ * @state: atomic state
+ * @encoder: DRM encoder
+ *
+ * This function adds all bridges attached to @encoder. This is needed to add
+ * bridge states to @state and make them available when
+ * &bridge_funcs.atomic_{check,pre_enable,enable,disable_post_disable}() are
+ * called
+ *
+ * Returns:
+ * 0 on success or can fail with -EDEADLK or -ENOMEM. When the error is EDEADLK
+ * then the w/w mutex code has detected a deadlock and the entire atomic
+ * sequence must be restarted. All other errors are fatal.
+ */
+int
+drm_atomic_add_encoder_bridges(struct drm_atomic_state *state,
+			       struct drm_encoder *encoder)
+{
+	struct drm_bridge_state *bridge_state;
+	struct drm_bridge *bridge;
+
+	if (!encoder)
+		return 0;
+
+	DRM_DEBUG_ATOMIC("Adding all bridges for [encoder:%d:%s] to %p\n",
+			 encoder->base.id, encoder->name, state);
+
+	drm_for_each_bridge_in_chain(encoder, bridge) {
+		bridge_state = drm_atomic_get_bridge_state(state, bridge);
+		if (IS_ERR(bridge_state))
+			return PTR_ERR(bridge_state);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_atomic_add_encoder_bridges);
+
 /**
  * drm_atomic_add_affected_connectors - add connectors for CRTC
  * @state: atomic state