drm/atomic-helper: Add {begin,end}_fb_access to plane helpers

Add {begin,end}_fb_access helpers to run at the beginning and end of
an atomic commit. The begin_fb_access helper acquires resources that
are necessary to perform the atomic commit. It it similar to prepare_fb,
except that the resources are to be released at the end of the commit.
Resources acquired by prepare_fb are held until after the next pageflip.

The end_fb_access helper performs the corresponding resource cleanup.
Atomic helpers call it with the new plane state. This is different from
cleanup_fb, which releases resources of the old plane state.

v2:
	* fix typos in commit message (Javier)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221025101737.8874-2-tzimmermann@suse.de

drivers/gpu/drm/drm_atomic_helper.c

@@ -2536,7 +2536,7 @@ int drm_atomic_helper_prepare_planes(struct drm_device *dev,
 		if (funcs->prepare_fb) {
 			ret = funcs->prepare_fb(plane, new_plane_state);
 			if (ret)
-				goto fail;
+				goto fail_prepare_fb;
 		} else {
 			WARN_ON_ONCE(funcs->cleanup_fb);
 
@@ -2545,13 +2545,34 @@ int drm_atomic_helper_prepare_planes(struct drm_device *dev,
 
 			ret = drm_gem_plane_helper_prepare_fb(plane, new_plane_state);
 			if (ret)
-				goto fail;
+				goto fail_prepare_fb;
+		}
+	}
+
+	for_each_new_plane_in_state(state, plane, new_plane_state, i) {
+		const struct drm_plane_helper_funcs *funcs = plane->helper_private;
+
+		if (funcs->begin_fb_access) {
+			ret = funcs->begin_fb_access(plane, new_plane_state);
+			if (ret)
+				goto fail_begin_fb_access;
 		}
 	}
 
 	return 0;
 
-fail:
+fail_begin_fb_access:
+	for_each_new_plane_in_state(state, plane, new_plane_state, j) {
+		const struct drm_plane_helper_funcs *funcs = plane->helper_private;
+
+		if (j >= i)
+			continue;
+
+		if (funcs->end_fb_access)
+			funcs->end_fb_access(plane, new_plane_state);
+	}
+	i = j; /* set i to upper limit to cleanup all planes */
+fail_prepare_fb:
 	for_each_new_plane_in_state(state, plane, new_plane_state, j) {
 		const struct drm_plane_helper_funcs *funcs;
 
@@ -2827,6 +2848,13 @@ void drm_atomic_helper_cleanup_planes(struct drm_device *dev,
 	struct drm_plane_state *old_plane_state, *new_plane_state;
 	int i;
 
+	for_each_oldnew_plane_in_state(old_state, plane, old_plane_state, new_plane_state, i) {
+		const struct drm_plane_helper_funcs *funcs = plane->helper_private;
+
+		if (funcs->end_fb_access)
+			funcs->end_fb_access(plane, new_plane_state);
+	}
+
 	for_each_oldnew_plane_in_state(old_state, plane, old_plane_state, new_plane_state, i) {
 		const struct drm_plane_helper_funcs *funcs;
 		struct drm_plane_state *plane_state;

drivers/gpu/drm/drm_gem_atomic_helper.c

@@ -414,16 +414,14 @@ void drm_gem_cleanup_shadow_fb(struct drm_plane *plane, struct drm_plane_state *
 EXPORT_SYMBOL(drm_gem_cleanup_shadow_fb);
 
 /**
- * drm_gem_simple_kms_prepare_shadow_fb - prepares shadow framebuffers
+ * drm_gem_simple_kms_begin_shadow_fb_access - prepares shadow framebuffers for CPU access
  * @pipe: the simple display pipe
  * @plane_state: the plane state of type struct drm_shadow_plane_state
  *
- * This function implements struct drm_simple_display_funcs.prepare_fb. It
+ * This function implements struct drm_simple_display_funcs.begin_fb_access.
- * maps all buffer objects of the plane's framebuffer into kernel address
- * space and stores them in struct drm_shadow_plane_state.map. The
- * framebuffer will be synchronized as part of the atomic commit.
  *
- * See drm_gem_simple_kms_cleanup_shadow_fb() for cleanup.
+ * See drm_gem_begin_shadow_fb_access() for details and
+ * drm_gem_simple_kms_cleanup_shadow_fb() for cleanup.
  *
  * Returns:
  * 0 on success, or a negative errno code otherwise.
@@ -436,14 +434,15 @@ int drm_gem_simple_kms_prepare_shadow_fb(struct drm_simple_display_pipe *pipe,
 EXPORT_SYMBOL(drm_gem_simple_kms_prepare_shadow_fb);
 
 /**
- * drm_gem_simple_kms_cleanup_shadow_fb - releases shadow framebuffers
+ * drm_gem_simple_kms_end_shadow_fb_access - releases shadow framebuffers from CPU access
  * @pipe: the simple display pipe
  * @plane_state: the plane state of type struct drm_shadow_plane_state
  *
- * This function implements struct drm_simple_display_funcs.cleanup_fb.
+ * This function implements struct drm_simple_display_funcs.end_fb_access.
- * This function unmaps all buffer objects of the plane's framebuffer.
+ * It undoes all effects of drm_gem_simple_kms_begin_shadow_fb_access() in
+ * reverse order.
  *
- * See drm_gem_simple_kms_prepare_shadow_fb().
+ * See drm_gem_simple_kms_begin_shadow_fb_access().
  */
 void drm_gem_simple_kms_cleanup_shadow_fb(struct drm_simple_display_pipe *pipe,
 					  struct drm_plane_state *plane_state)

drivers/gpu/drm/drm_simple_kms_helper.c

@@ -285,6 +285,30 @@ static void drm_simple_kms_plane_cleanup_fb(struct drm_plane *plane,
 	pipe->funcs->cleanup_fb(pipe, state);
 }
 
+static int drm_simple_kms_plane_begin_fb_access(struct drm_plane *plane,
+						struct drm_plane_state *new_plane_state)
+{
+	struct drm_simple_display_pipe *pipe;
+
+	pipe = container_of(plane, struct drm_simple_display_pipe, plane);
+	if (!pipe->funcs || !pipe->funcs->begin_fb_access)
+		return 0;
+
+	return pipe->funcs->begin_fb_access(pipe, new_plane_state);
+}
+
+static void drm_simple_kms_plane_end_fb_access(struct drm_plane *plane,
+					       struct drm_plane_state *new_plane_state)
+{
+	struct drm_simple_display_pipe *pipe;
+
+	pipe = container_of(plane, struct drm_simple_display_pipe, plane);
+	if (!pipe->funcs || !pipe->funcs->end_fb_access)
+		return;
+
+	pipe->funcs->end_fb_access(pipe, new_plane_state);
+}
+
 static bool drm_simple_kms_format_mod_supported(struct drm_plane *plane,
 						uint32_t format,
 						uint64_t modifier)
@@ -295,6 +319,8 @@ static bool drm_simple_kms_format_mod_supported(struct drm_plane *plane,
 static const struct drm_plane_helper_funcs drm_simple_kms_plane_helper_funcs = {
 	.prepare_fb = drm_simple_kms_plane_prepare_fb,
 	.cleanup_fb = drm_simple_kms_plane_cleanup_fb,
+	.begin_fb_access = drm_simple_kms_plane_begin_fb_access,
+	.end_fb_access = drm_simple_kms_plane_end_fb_access,
 	.atomic_check = drm_simple_kms_plane_atomic_check,
 	.atomic_update = drm_simple_kms_plane_atomic_update,
 };

include/drm/drm_modeset_helper_vtables.h

@@ -1184,11 +1184,20 @@ struct drm_plane_helper_funcs {
 	 * can call drm_gem_plane_helper_prepare_fb() from their @prepare_fb
 	 * hook.
 	 *
+	 * The resources acquired in @prepare_fb persist after the end of
+	 * the atomic commit. Resources that can be release at the commit's end
+	 * should be acquired in @begin_fb_access and released in @end_fb_access.
+	 * For example, a GEM buffer's pin operation belongs into @prepare_fb to
+	 * keep the buffer pinned after the commit. But a vmap operation for
+	 * shadow-plane helpers belongs into @begin_fb_access, so that atomic
+	 * helpers remove the mapping at the end of the commit.
+	 *
 	 * The helpers will call @cleanup_fb with matching arguments for every
 	 * successful call to this hook.
 	 *
 	 * This callback is used by the atomic modeset helpers and by the
-	 * transitional plane helpers, but it is optional.
+	 * transitional plane helpers, but it is optional. See @begin_fb_access
+	 * for preparing per-commit resources.
 	 *
 	 * RETURNS:
 	 *
@@ -1211,6 +1220,36 @@ struct drm_plane_helper_funcs {
 	void (*cleanup_fb)(struct drm_plane *plane,
 			   struct drm_plane_state *old_state);
 
+	/**
+	 * @begin_fb_access:
+	 *
+	 * This hook prepares the plane for access during an atomic commit.
+	 * In contrast to @prepare_fb, resources acquired in @begin_fb_access,
+	 * are released at the end of the atomic commit in @end_fb_access.
+	 *
+	 * For example, with shadow-plane helpers, the GEM buffer's vmap
+	 * operation belongs into @begin_fb_access, so that the buffer's
+	 * memory will be unmapped at the end of the commit in @end_fb_access.
+	 * But a GEM buffer's pin operation belongs into @prepare_fb
+	 * to keep the buffer pinned after the commit.
+	 *
+	 * The callback is used by the atomic modeset helpers, but it is optional.
+	 * See @end_fb_cleanup for undoing the effects of @begin_fb_access and
+	 * @prepare_fb for acquiring resources until the next pageflip.
+	 *
+	 * Returns:
+	 * 0 on success, or a negative errno code otherwise.
+	 */
+	int (*begin_fb_access)(struct drm_plane *plane, struct drm_plane_state *new_plane_state);
+
+	/**
+	 * @end_fb_access:
+	 *
+	 * This hook cleans up resources allocated by @begin_fb_access. It it called
+	 * at the end of a commit for the new plane state.
+	 */
+	void (*end_fb_access)(struct drm_plane *plane, struct drm_plane_state *new_plane_state);
+
 	/**
 	 * @atomic_check:
 	 *

include/drm/drm_simple_kms_helper.h

@@ -135,6 +135,26 @@ struct drm_simple_display_pipe_funcs {
 	void (*cleanup_fb)(struct drm_simple_display_pipe *pipe,
 			   struct drm_plane_state *plane_state);
 
+	/**
+	 * @begin_fb_access:
+	 *
+	 * Optional, called by &drm_plane_helper_funcs.begin_fb_access. Please read
+	 * the documentation for the &drm_plane_helper_funcs.begin_fb_access hook for
+	 * more details.
+	 */
+	int (*begin_fb_access)(struct drm_simple_display_pipe *pipe,
+			       struct drm_plane_state *new_plane_state);
+
+	/**
+	 * @end_fb_access:
+	 *
+	 * Optional, called by &drm_plane_helper_funcs.end_fb_access. Please read
+	 * the documentation for the &drm_plane_helper_funcs.end_fb_access hook for
+	 * more details.
+	 */
+	void (*end_fb_access)(struct drm_simple_display_pipe *pipe,
+			      struct drm_plane_state *plane_state);
+
 	/**
 	 * @enable_vblank:
 	 *