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

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 30.05.26 um 15:59 schrieb Maxime Ripard:
> 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);

This needs to remain for now, right?

Best regards
Thomas

> +	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)
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)