drm/atomic: Convert __drm_atomic_get_current_plane_state() to modern accessor

The __drm_atomic_get_current_plane_state() function tries to get and
return the existing plane state, and if it doesn't exist returns the one
stored in the drm_plane->state field.

Using the current nomenclature, it tries to get the existing plane state
with an ad-hoc implementation of drm_atomic_get_existing_plane_state(),
and falls back to either the old or new plane state, depending on
whether it is called before or after drm_atomic_helper_swap_state().

The existing plane state itself is deprecated, because it also changes
when swapping states from the new state to the old state.

Fortunately for us, we can simplify things. Indeed,
__drm_atomic_get_current_plane_state() is only used in two macros:
intel_atomic_crtc_state_for_each_plane_state and
drm_atomic_crtc_state_for_each_plane_state().

The intel variant is only used through the intel_wm_compute() function
that is only ever called in intel_crtc_atomic_check().

The generic variant is more widely used, and can be found in the malidp,
msm, tegra and vc4 drivers. All of these call sites though are during
atomic_check(), so we end up in the same situation than Intel's.

Thus, we only ever use the existing state as the new state, and
plane->state is always going to be the old state. Any plane isn't
guaranteed to be part of the state though, so we can't rely on
drm_atomic_get_old_plane_state() and we still need to use plane->state.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/20250930-drm-no-more-existing-state-v5-4-eeb9e1287907@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

1 files changed, 13 insertions, 7 deletions

diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index fe47715c31e4..c8b88990506e 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -793,11 +793,11 @@ drm_atomic_get_new_connector_state(const struct drm_atomic_state *state,
  * @state: global atomic state object
  * @plane: plane to grab
  *
- * This function returns the plane state for the given plane, either from
- * @state, or if the plane isn't part of the atomic state update, from @plane.
- * This is useful in atomic check callbacks, when drivers need to peek at, but
- * not change, state of other planes, since it avoids threading an error code
- * back up the call chain.
+ * This function returns the plane state for the given plane, either the
+ * new plane state from @state, or if the plane isn't part of the atomic
+ * state update, from @plane. This is useful in atomic check callbacks,
+ * when drivers need to peek at, but not change, state of other planes,
+ * since it avoids threading an error code back up the call chain.
  *
  * WARNING:
  *
@@ -818,9 +818,15 @@ static inline const struct drm_plane_state *
 __drm_atomic_get_current_plane_state(const struct drm_atomic_state *state,
 				     struct drm_plane *plane)
 {
-	if (state->planes[drm_plane_index(plane)].state)
-		return state->planes[drm_plane_index(plane)].state;
+	struct drm_plane_state *plane_state;
 
+	plane_state = drm_atomic_get_new_plane_state(state, plane);
+	if (plane_state)
+		return plane_state;
+
+	/*
+	 * If the plane isn't part of the state, fallback to the currently active one.
+	 */
 	return plane->state;
 }