[PATCH 04/76] drm/bridge: Add new atomic_create_state callback

[Maxime Ripard <mripard@kernel.org>]

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.

Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
 drivers/gpu/drm/drm_bridge.c |  8 ++++++--
 include/drm/drm_bridge.h     | 33 +++++++++++----------------------
 2 files changed, 17 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 687b36eea0c7..ef06c1aa509a 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -498,11 +498,14 @@ static struct drm_private_state *
 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);
 
 	return &state->base;
 }
@@ -513,11 +516,12 @@ static const struct drm_private_state_funcs drm_bridge_priv_state_funcs = {
 	.atomic_destroy_state = drm_bridge_atomic_destroy_priv_state,
 };
 
 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);
 }
 
 /**
  * drm_bridge_attach - attach the bridge to an encoder's chain
  *
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index 4ba3a5deef9a..a6c07d339afa 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -502,35 +502,24 @@ struct drm_bridge_funcs {
 			    struct drm_bridge_state *bridge_state,
 			    struct drm_crtc_state *crtc_state,
 			    struct drm_connector_state *conn_state);
 
 	/**
-	 * @atomic_reset:
+	 * @atomic_create_state:
 	 *
-	 * Reset the bridge to a predefined state (or retrieve its current
-	 * state) and return a &drm_bridge_state object matching this state.
-	 * This function is called at attach time.
-	 *
-	 * The atomic_reset hook is mandatory if the bridge implements any of
-	 * the atomic hooks, and should be left unassigned otherwise. For
-	 * bridges that don't subclass &drm_bridge_state, the
-	 * drm_atomic_helper_bridge_reset() helper function shall be used to
-	 * implement this hook.
-	 *
-	 * Note that the atomic_reset() semantics is not exactly matching the
-	 * reset() semantics found on other components (connector, plane, ...).
-	 *
-	 * 1. The reset operation happens when the bridge is attached, not when
-	 *    drm_mode_config_reset() is called
-	 * 2. It's meant to be used exclusively on bridges that have been
-	 *    converted to the ATOMIC API
+	 * 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 valid drm_bridge_state object in case of success, an ERR_PTR()
-	 * giving the reason of the failure otherwise.
+	 *
+	 * A new, pristine, bridge state instance or an error pointer
+	 * on failure.
 	 */
-	struct drm_bridge_state *(*atomic_reset)(struct drm_bridge *bridge);
+	struct drm_bridge_state *(*atomic_create_state)(struct drm_bridge *bridge);
 
 	/**
 	 * @detect:
 	 *
 	 * Check if anything is attached to the bridge output.
@@ -1369,11 +1358,11 @@ drm_bridge_get_current_state(struct drm_bridge *bridge)
 	/*
 	 * Only atomic bridges will have bridge->base initialized by
 	 * 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_create_state)
 		return NULL;
 
 	drm_modeset_lock_assert_held(&bridge->base.lock);
 
 	if (!bridge->base.state)

-- 
2.54.0