drm/atomic-helper: Implement drm_atomic_helper_duplicate_state()

This function can be used to duplicate an atomic state object. This is
useful for example to implement suspend/resume, where the state before
suspend can be saved and restored upon resume.

v2: move locking to caller, be more explicit about prerequisites
v3: explicitly pass lock acquisition context, improve kerneldoc

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_atomic_helper.c

@@ -2371,6 +2371,84 @@ drm_atomic_helper_connector_duplicate_state(struct drm_connector *connector)
 }
 EXPORT_SYMBOL(drm_atomic_helper_connector_duplicate_state);
 
+/**
+ * drm_atomic_helper_duplicate_state - duplicate an atomic state object
+ * @dev: DRM device
+ * @ctx: lock acquisition context
+ *
+ * Makes a copy of the current atomic state by looping over all objects and
+ * duplicating their respective states.
+ *
+ * Note that this treats atomic state as persistent between save and restore.
+ * Drivers must make sure that this is possible and won't result in confusion
+ * or erroneous behaviour.
+ *
+ * Note that if callers haven't already acquired all modeset locks this might
+ * return -EDEADLK, which must be handled by calling drm_modeset_backoff().
+ *
+ * Returns:
+ * A pointer to the copy of the atomic state object on success or an
+ * ERR_PTR()-encoded error code on failure.
+ */
+struct drm_atomic_state *
+drm_atomic_helper_duplicate_state(struct drm_device *dev,
+				  struct drm_modeset_acquire_ctx *ctx)
+{
+	struct drm_atomic_state *state;
+	struct drm_connector *conn;
+	struct drm_plane *plane;
+	struct drm_crtc *crtc;
+	int err = 0;
+
+	state = drm_atomic_state_alloc(dev);
+	if (!state)
+		return ERR_PTR(-ENOMEM);
+
+	state->acquire_ctx = ctx;
+
+	drm_for_each_crtc(crtc, dev) {
+		struct drm_crtc_state *crtc_state;
+
+		crtc_state = drm_atomic_get_crtc_state(state, crtc);
+		if (IS_ERR(crtc_state)) {
+			err = PTR_ERR(crtc_state);
+			goto free;
+		}
+	}
+
+	drm_for_each_plane(plane, dev) {
+		struct drm_plane_state *plane_state;
+
+		plane_state = drm_atomic_get_plane_state(state, plane);
+		if (IS_ERR(plane_state)) {
+			err = PTR_ERR(plane_state);
+			goto free;
+		}
+	}
+
+	drm_for_each_connector(conn, dev) {
+		struct drm_connector_state *conn_state;
+
+		conn_state = drm_atomic_get_connector_state(state, conn);
+		if (IS_ERR(conn_state)) {
+			err = PTR_ERR(conn_state);
+			goto free;
+		}
+	}
+
+	/* clear the acquire context so that it isn't accidentally reused */
+	state->acquire_ctx = NULL;
+
+free:
+	if (err < 0) {
+		drm_atomic_state_free(state);
+		state = ERR_PTR(err);
+	}
+
+	return state;
+}
+EXPORT_SYMBOL(drm_atomic_helper_duplicate_state);
+
 /**
  * __drm_atomic_helper_connector_destroy_state - release connector state
  * @connector: connector object

include/drm/drm_atomic_helper.h

@@ -118,6 +118,9 @@ __drm_atomic_helper_connector_duplicate_state(struct drm_connector *connector,
 					   struct drm_connector_state *state);
 struct drm_connector_state *
 drm_atomic_helper_connector_duplicate_state(struct drm_connector *connector);
+struct drm_atomic_state *
+drm_atomic_helper_duplicate_state(struct drm_device *dev,
+				  struct drm_modeset_acquire_ctx *ctx);
 void
 __drm_atomic_helper_connector_destroy_state(struct drm_connector *connector,
 					    struct drm_connector_state *state);