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>

3 files changed, 27 insertions, 5 deletions

diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
index f0688f2d83fe..9dfb9b6ba392 100644
--- a/drivers/gpu/drm/drm_atomic_state_helper.c
+++ b/drivers/gpu/drm/drm_atomic_state_helper.c
@@ -894,8 +894,9 @@ EXPORT_SYMBOL(drm_atomic_helper_bridge_destroy_state);
  * @state is assumed to be zeroed.
  *
  * Initializes the bridge state to default values. This is meant to be called
- * by the bridge &drm_bridge_funcs.atomic_reset hook for bridges that subclass
- * the bridge state.
+ * by the bridge &drm_bridge_funcs.atomic_create_state or
+ * &drm_bridge_funcs.atomic_reset hook for bridges that subclass the bridge
+ * state.
  */
 void __drm_atomic_helper_bridge_state_init(struct drm_bridge_state *state,
 					   struct drm_bridge *bridge)
diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 1daac8a7f4c9..776856e23592 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -542,7 +542,10 @@ drm_bridge_atomic_create_priv_state(struct drm_private_obj *obj)
 	struct drm_bridge *bridge = drm_priv_to_bridge(obj);
 	struct drm_bridge_state *state;
 
-	state = bridge->funcs->atomic_reset(bridge);
+	if (bridge->funcs->atomic_create_state)
+		state = bridge->funcs->atomic_create_state(bridge);
+	else
+		state = bridge->funcs->atomic_reset(bridge);
 	if (IS_ERR(state))
 		return ERR_CAST(state);
 
@@ -557,7 +560,8 @@ static const struct drm_private_state_funcs drm_bridge_priv_state_funcs = {
 
 static bool drm_bridge_is_atomic(struct drm_bridge *bridge)
 {
-	return bridge->funcs->atomic_reset != NULL;
+	return (bridge->funcs->atomic_create_state ||
+		bridge->funcs->atomic_reset);
 }
 
 /**
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);