Re: [PATCH 05/14] drm/plane: Add new atomic_create_state callback

[Tomi Valkeinen]

Hi,

On 10/03/2026 18:06, Maxime Ripard wrote:
> Commit 47b5ac7daa46 ("drm/atomic: Add new atomic_create_state callback
> to drm_private_obj") introduced a new pattern for allocating drm object
> states.
> 
> Instead of relying on the reset() callback, it created a new
> atomic_create_state hook. This is helpful because reset is a bit
> overloaded: it's used to create the initial software tate, reset it, but
> also reset the hardware.
> 
> It can also be used either at probe time, to create the initial state
> and possibly reset the hardware to an expected default, but also during
> suspend/resume.
> 
> Both these cases come with different expectations too: during the
> initialization, we want to initialize all states, but during
> suspend/resume, drm_private_states for example are expected to be kept
> around.
> 
> And reset() isn't fallible, which makes it harder to handle
> initialization errors properly.
> 
> And this is only really relevant for some drivers, since all the helpers
> for reset only create a new state, and don't touch the hardware at all.
> 
> It was thus decided to create a new hook that would allocate and
> initialize a pristine state without any side effect:
> atomic_create_state to untangle a bit some of it, and to separate the
> initialization with the actual reset one might need during a
> suspend/resume.
> 
> Let's continue the transition to the new pattern with planes.
> 
> Signed-off-by: Maxime Ripard <mripard@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_atomic_state_helper.c | 41 +++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_mode_config.c         | 18 ++++++++++++++
>  include/drm/drm_atomic_state_helper.h     |  4 +++
>  include/drm/drm_plane.h                   | 13 ++++++++++
>  4 files changed, 76 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
> index a1abf4247c348eca21da348c3893dd843b9ed391..898e168eeae1c3899121ffd13c79fae7803fcd2a 100644
> --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> @@ -318,10 +318,29 @@ void __drm_atomic_helper_plane_reset(struct drm_plane *plane,
>  
>  	plane->state = plane_state;
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_plane_reset);
>  
> +/**
> + * __drm_atomic_helper_plane_create_state - initializes plane state
> + * @plane: plane object
> + * @state: new state to initialize
> + *
> + * Initializes the newly allocated @state, usually required when
> + * initializing the drivers.
> + *
> + * @state is assumed to be zeroed.
> + *
> + * This is useful for drivers that subclass @drm_plane_state.
> + */
> +void __drm_atomic_helper_plane_create_state(struct drm_plane *plane,
> +					    struct drm_plane_state *state)
> +{
> +	__drm_atomic_helper_plane_reset(plane, state);
> +}
> +EXPORT_SYMBOL(__drm_atomic_helper_plane_create_state);
> +

This calls __drm_atomic_helper_plane_reset(), which does "plane->state =
plane_state". From the description I understood this would be without
side effects. Is that not a side effect? Or should this call
__drm_atomic_helper_plane_state_reset() instead?

Same thing for the next two patches too.

>  /**
>   * drm_atomic_helper_plane_reset - default &drm_plane_funcs.reset hook for planes
>   * @plane: drm plane
>   *
>   * Resets the atomic state for @plane by freeing the state pointer (which might
> @@ -337,10 +356,32 @@ void drm_atomic_helper_plane_reset(struct drm_plane *plane)
>  	if (plane->state)
>  		__drm_atomic_helper_plane_reset(plane, plane->state);
>  }
>  EXPORT_SYMBOL(drm_atomic_helper_plane_reset);
>  
> +/**
> + * drm_atomic_helper_plane_create_state - default &drm_plane_funcs.atomic_create_state hook for planes
> + * @plane: plane object
> + *
> + * Initializes a pristine @drm_plane_state.
> + *
> + * This is useful for drivers that don't subclass @drm_plane_state.
> + */
> +struct drm_plane_state *drm_atomic_helper_plane_create_state(struct drm_plane *plane)
> +{
> +	struct drm_plane_state *state;
> +
> +	state = kzalloc_obj(*state);
> +	if (!state)
> +		return ERR_PTR(-ENOMEM);
> +
> +	__drm_atomic_helper_plane_reset(plane, state);
> +
> +	return state;
> +}
> +EXPORT_SYMBOL(drm_atomic_helper_plane_create_state);
> +
>  /**
>   * __drm_atomic_helper_plane_duplicate_state - copy atomic plane state
>   * @plane: plane object
>   * @state: atomic plane state
>   *
> diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> index 54c27376f9894ef5eee378bb5b1e5fc7049de922..43fe64540b8ec4df4bb823d96db607e6bfe58824 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -180,10 +180,26 @@ int drm_mode_getresources(struct drm_device *dev, void *data,
>  	drm_connector_list_iter_end(&conn_iter);
>  
>  	return ret;
>  }
>  
> +static int drm_mode_config_plane_create_state(struct drm_plane *plane)
> +{
> +	struct drm_plane_state *plane_state;
> +
> +	if (!plane->funcs->atomic_create_state)
> +		return 0;
> +
> +	plane_state = plane->funcs->atomic_create_state(plane);
> +	if (IS_ERR(plane_state))
> +		return PTR_ERR(plane_state);
> +
> +	plane->state = plane_state;

And this one sets the plane->state, so maybe .atomic_create_state() is
not supposed to do that.

> +
> +	return 0;
> +}
> +
>  /**
>   * drm_mode_config_reset - call ->reset callbacks
>   * @dev: drm device
>   *
>   * This functions calls all the crtc's, encoder's and connector's ->reset
> @@ -207,10 +223,12 @@ void drm_mode_config_reset(struct drm_device *dev)
>  		drm_colorop_reset(colorop);
>  
>  	drm_for_each_plane(plane, dev)
>  		if (plane->funcs->reset)
>  			plane->funcs->reset(plane);
> +		else if (plane->funcs->atomic_create_state)
> +			drm_mode_config_plane_create_state(plane);
>  
>  	drm_for_each_crtc(crtc, dev)
>  		if (crtc->funcs->reset)
>  			crtc->funcs->reset(crtc);
>  
> diff --git a/include/drm/drm_atomic_state_helper.h b/include/drm/drm_atomic_state_helper.h
> index 900672c6ea90ba9cb87e38a7c84225972aee43c5..f56a91fca20e778d8ccb1767301dc00783bf40f3 100644
> --- a/include/drm/drm_atomic_state_helper.h
> +++ b/include/drm/drm_atomic_state_helper.h
> @@ -51,12 +51,16 @@ struct drm_crtc_state *
>  drm_atomic_helper_crtc_duplicate_state(struct drm_crtc *crtc);
>  void __drm_atomic_helper_crtc_destroy_state(struct drm_crtc_state *state);
>  void drm_atomic_helper_crtc_destroy_state(struct drm_crtc *crtc,
>  					  struct drm_crtc_state *state);
>  
> +void __drm_atomic_helper_plane_create_state(struct drm_plane *plane,
> +					    struct drm_plane_state *state);
>  void __drm_atomic_helper_plane_state_reset(struct drm_plane_state *state,
>  					   struct drm_plane *plane);
> +struct drm_plane_state *
> +drm_atomic_helper_plane_create_state(struct drm_plane *plane);
>  void __drm_atomic_helper_plane_reset(struct drm_plane *plane,
>  				     struct drm_plane_state *state);
>  void drm_atomic_helper_plane_reset(struct drm_plane *plane);
>  void __drm_atomic_helper_plane_duplicate_state(struct drm_plane *plane,
>  					       struct drm_plane_state *state);
> diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> index 703ef4d1bbbcf084c43aa5e127d28691878061c4..4d4d511b681d50c17fbc593cce9f706d63e04a52 100644
> --- a/include/drm/drm_plane.h
> +++ b/include/drm/drm_plane.h
> @@ -386,10 +386,23 @@ struct drm_plane_funcs {
>  	 * 0 on success or a negative error code on failure.
>  	 */
>  	int (*set_property)(struct drm_plane *plane,
>  			    struct drm_property *property, uint64_t val);
>  
> +	/**
> +	 * @atomic_create_state:
> +	 *
> +	 * Allocates a pristine, initialized, state for the plane object
> +	 * and returns it.
> +	 *
> +	 * RETURNS:
> +	 *
> +	 * A new, pristine, plane state instance or an error pointer
> +	 * on failure.
> +	 */
> +	struct drm_plane_state *(*atomic_create_state)(struct drm_plane *plane);
> +
>  	/**
>  	 * @atomic_duplicate_state:
>  	 *
>  	 * Duplicate the current atomic state for this plane and return it.
>  	 * The core and helpers guarantee that any atomic state duplicated with
>