drm/atomic-helper: Add private_obj atomic_create_state helper

Now that we have an atomic_create_state callback for drm_private_objs,
we can provide a helper for it.

It's somewhat different from the other similar helpers though, because
we definitely expect drm_private_obj to be subclassed. It wouldn't make
sense for a driver to use it as-is.

So we can't provide a straight implementation of the atomic_create_state
callback, but rather we provide the parts that will deal with the
drm_private_obj initialization, and we will leave the allocation and
initialization of the subclass to drivers.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patch.msgid.link/20260128-drm-private-obj-reset-v4-3-90891fa3d3b0@redhat.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>

drivers/gpu/drm/drm_atomic_state_helper.c

@@ -714,6 +714,28 @@ void drm_atomic_helper_connector_destroy_state(struct drm_connector *connector,
 }
 EXPORT_SYMBOL(drm_atomic_helper_connector_destroy_state);
 
+/**
+ * __drm_atomic_helper_private_obj_create_state - initializes private object state
+ * @obj: private object
+ * @state: new state to initialize
+ *
+ * Initializes the newly allocated @state, usually required when
+ * initializing the drivers.
+ *
+ * @obj is assumed to be zeroed.
+ *
+ * This is useful for drivers that use private states.
+ */
+void __drm_atomic_helper_private_obj_create_state(struct drm_private_obj *obj,
+						  struct drm_private_state *state)
+{
+	if (state)
+		state->obj = obj;
+
+	obj->state = state;
+}
+EXPORT_SYMBOL(__drm_atomic_helper_private_obj_create_state);
+
 /**
  * __drm_atomic_helper_private_obj_duplicate_state - copy atomic private state
  * @obj: CRTC object

include/drm/drm_atomic_state_helper.h

@@ -84,6 +84,9 @@ void
 __drm_atomic_helper_connector_destroy_state(struct drm_connector_state *state);
 void drm_atomic_helper_connector_destroy_state(struct drm_connector *connector,
 					  struct drm_connector_state *state);
+
+void __drm_atomic_helper_private_obj_create_state(struct drm_private_obj *obj,
+						  struct drm_private_state *state);
 void __drm_atomic_helper_private_obj_duplicate_state(struct drm_private_obj *obj,
 						     struct drm_private_state *state);