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.

v10:
* Add changelog to the commit message

v9:
* Clarify the fact that the bridge->atomic_reset() and
  {connector,plane,crtc,...}->reset() semantics are different
* Move the drm_atomic_private_obj_init() call back to
  drm_bridge_attach()
* Check the presence of ->atomic_duplicate_state instead of
  ->atomic_reset in drm_atomic_add_encoder_bridges()
* Fix copy&paste errors in the atomic bridge state helpers doc
* Add A-b/R-b tags

v8:
* Move bridge state helpers out of the CONFIG_DEBUGFS section

v7:
* Move helpers, struct-defs, ... to atomic helper files to avoid the
  drm -> drm_kms_helper -> drm circular dep
* Stop providing default implementation for atomic state reset,
  duplicate and destroy hooks (has to do with the helper/core split)
* Drop all R-b/T-b as helpers have now be moved to other places

v6:
* Made helpers private, removed doc and moved them to satisfy dependencies
* Renamed helpers to _default_

v5:
* Re-introduced the helpers from v4

v4:
* Fix the doc
* Kill default helpers (inlined)
* Fix drm_atomic_get_bridge_state() to check for an ERR_PTR()
* Add Neil's R-b

v3:
* No changes

v2:
* Use drm_for_each_bridge_in_chain()
* Rename helpers to be more consistent with the rest of the DRM API
* Improve/fix the doc

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200128135514.108171-2-boris.brezillon@collabora.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 +1018,121 @@ static void drm_atomic_connector_print_state(struct drm_printer *p,
 		connector->funcs->atomic_print_state(p, state);
 }
 
+/**
+ * drm_atomic_get_bridge_state - get bridge state
+ * @state: global atomic state object
+ * @bridge: bridge to get state object for
+ *
+ * This function returns the bridge state for the given bridge, allocating it
+ * if needed. It will also grab the relevant bridge lock to make sure that the
+ * state is consistent.
+ *
+ * Returns:
+ *
+ * Either the allocated state or the error code encoded into the pointer. When
+ * the error is EDEADLK then the w/w mutex code has detected a deadlock and the
+ * entire atomic sequence must be restarted.
+ */
+struct drm_bridge_state *
+drm_atomic_get_bridge_state(struct drm_atomic_state *state,
+			    struct drm_bridge *bridge)
+{
+	struct drm_private_state *obj_state;
+
+	obj_state = drm_atomic_get_private_obj_state(state, &bridge->base);
+	if (IS_ERR(obj_state))
+		return ERR_CAST(obj_state);
+
+	return drm_priv_to_bridge_state(obj_state);
+}
+EXPORT_SYMBOL(drm_atomic_get_bridge_state);
+
+/**
+ * drm_atomic_get_old_bridge_state - get old bridge state, if it exists
+ * @state: global atomic state object
+ * @bridge: bridge to grab
+ *
+ * This function returns the old bridge state for the given bridge, or NULL if
+ * the bridge is not part of the global atomic state.
+ */
+struct drm_bridge_state *
+drm_atomic_get_old_bridge_state(struct drm_atomic_state *state,
+				struct drm_bridge *bridge)
+{
+	struct drm_private_state *obj_state;
+
+	obj_state = drm_atomic_get_old_private_obj_state(state, &bridge->base);
+	if (!obj_state)
+		return NULL;
+
+	return drm_priv_to_bridge_state(obj_state);
+}
+EXPORT_SYMBOL(drm_atomic_get_old_bridge_state);
+
+/**
+ * drm_atomic_get_new_bridge_state - get new bridge state, if it exists
+ * @state: global atomic state object
+ * @bridge: bridge to grab
+ *
+ * This function returns the new bridge state for the given bridge, or NULL if
+ * the bridge is not part of the global atomic state.
+ */
+struct drm_bridge_state *
+drm_atomic_get_new_bridge_state(struct drm_atomic_state *state,
+				struct drm_bridge *bridge)
+{
+	struct drm_private_state *obj_state;
+
+	obj_state = drm_atomic_get_new_private_obj_state(state, &bridge->base);
+	if (!obj_state)
+		return NULL;
+
+	return drm_priv_to_bridge_state(obj_state);
+}
+EXPORT_SYMBOL(drm_atomic_get_new_bridge_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) {
+		/* Skip bridges that don't implement the atomic state hooks. */
+		if (!bridge->funcs->atomic_duplicate_state)
+			continue;
+
+		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