drm/bridge: Add new atomic_create_state callback

Commit 47b5ac7daa46 ("drm/atomic: Add new atomic_create_state callback
to drm_private_obj") introduced a new pattern for allocating drm object
states: atomic_create_state, a dedicated hook that allocates and
initializes a pristine state without any side effect.

The bridge atomic_reset callback is already fallible and in practice
only allocates and initializes state without touching hardware.
However, the reset name does not make this contract clear: callers
and implementers cannot tell from the name alone whether the hardware
will be affected or when the hook is safe to call.

Add an atomic_create_state callback to drm_bridge_funcs to make the
contract explicit: allocate a pristine state, initialize it, no side
effects. The core calls it when available, falling back to
atomic_reset otherwise.

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com> # imx8mp + sn65dsi84 + bridge hotplug
Link: https://patch.msgid.link/20260619-drm-no-more-bridge-reset-v3-6-ff399263111b@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

1 files changed, 18 insertions, 1 deletions

diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index 00a95f927e34..70e574fbf034 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -531,6 +531,22 @@ struct drm_bridge_funcs {
 	struct drm_bridge_state *(*atomic_reset)(struct drm_bridge *bridge);
 
 	/**
+	 * @atomic_create_state:
+	 *
+	 * Allocate a pristine, initialized, state for the bridge
+	 * object and return it. This callback must have no side
+	 * effects: in particular, the returned state must not be
+	 * assigned to the object's state pointer and it must not affect
+	 * the hardware state.
+	 *
+	 * RETURNS:
+	 *
+	 * A new, pristine, bridge state instance or an error pointer
+	 * on failure.
+	 */
+	struct drm_bridge_state *(*atomic_create_state)(struct drm_bridge *bridge);
+
+	/**
 	 * @detect:
 	 *
 	 * Check if anything is attached to the bridge output.
@@ -1375,7 +1391,8 @@ drm_bridge_get_current_state(struct drm_bridge *bridge)
 	 * drm_atomic_private_obj_init(), so we need to make sure we're
 	 * working with one before we try to use the lock.
 	 */
-	if (!bridge->funcs || !bridge->funcs->atomic_reset)
+	if (!bridge->funcs ||
+	    !(bridge->funcs->atomic_reset || bridge->funcs->atomic_create_state))
 		return NULL;
 
 	drm_modeset_lock_assert_held(&bridge->base.lock);