[PATCH 1/8] drm: Introduce an atomic_commit_setup function

[Maxime Ripard]

Private objects storing a state shared across all CRTCs need to be
carefully handled to avoid a use-after-free issue.

The proper way to do this to track all the commits using that shared
state and wait for the previous commits to be done before going on with
the current one to avoid the reordering of commits that could occur.

However, this commit setup needs to be done after
drm_atomic_helper_setup_commit(), because before the CRTC commit
structure hasn't been allocated before, and before the workqueue is
scheduled, because we would be potentially reordered already otherwise.

That means that drivers currently have to roll their own
drm_atomic_helper_commit() function, even though it would be identical
if not for the commit setup.

Let's introduce a hook to do so that would be called as part of
drm_atomic_helper_commit, allowing us to reuse the atomic helpers.

Suggested-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Maxime Ripard <maxime at cerno.tech>
---
 drivers/gpu/drm/drm_atomic_helper.c      |  6 ++++++
 include/drm/drm_modeset_helper_vtables.h | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index ddd0e3239150..7d69c7844dfc 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -2083,8 +2083,11 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
 	struct drm_plane *plane;
 	struct drm_plane_state *old_plane_state, *new_plane_state;
 	struct drm_crtc_commit *commit;
+	const struct drm_mode_config_helper_funcs *funcs;
 	int i, ret;
 
+	funcs = state->dev->mode_config.helper_private;
+
 	for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state, new_crtc_state, i) {
 		commit = kzalloc(sizeof(*commit), GFP_KERNEL);
 		if (!commit)
@@ -2169,6 +2172,9 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
 		new_plane_state->commit = drm_crtc_commit_get(commit);
 	}
 
+	if (funcs && funcs->atomic_commit_setup)
+		return funcs->atomic_commit_setup(state);
+
 	return 0;
 }
 EXPORT_SYMBOL(drm_atomic_helper_setup_commit);
diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index f2de050085be..56470baf0513 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -1396,6 +1396,24 @@ struct drm_mode_config_helper_funcs {
 	 * drm_atomic_helper_commit_tail().
 	 */
 	void (*atomic_commit_tail)(struct drm_atomic_state *state);
+
+	/**
+	 * @atomic_commit_setup:
+	 *
+	 * This hook is used by the default atomic_commit() hook implemented in
+	 * drm_atomic_helper_commit() together with the nonblocking helpers (see
+	 * drm_atomic_helper_setup_commit()) to extend the DRM commit setup. It
+	 * is not used by the atomic helpers.
+	 *
+	 * This function is called at the end of
+	 * drm_atomic_helper_setup_commit(), so once the commit has been
+	 * properly setup across the generic DRM object states. It allows
+	 * drivers to do some additional commit tracking that isn't related to a
+	 * CRTC, plane or connector, typically a private object.
+	 *
+	 * This hook is optional.
+	 */
+	int (*atomic_commit_setup)(struct drm_atomic_state *state);
 };
 
 #endif
-- 
2.28.0