[v3,10/20] drm/plane: 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.

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 state, 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.

reset() also isn't fallible, which makes it harder to handle
initialization errors properly. This is only really relevant for some
drivers though, 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.

Continue the transition to the new pattern with planes.

Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
 drivers/gpu/drm/drm_atomic_state_helper.c | 25 +++++++++++++++++++++++++
 drivers/gpu/drm/drm_mode_config.c         | 21 ++++++++++++++++++++-
 include/drm/drm_atomic_state_helper.h     |  2 ++
 include/drm/drm_plane.h                   | 16 ++++++++++++++++
 4 files changed, 63 insertions(+), 1 deletion(-)
  

Hi Maxime,

Thank you for the patch.

On Fri, Apr 24, 2026 at 12:18:50PM +0200, 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 state, 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.
> 
> reset() also isn't fallible, which makes it harder to handle
> initialization errors properly. This is only really relevant for some
> drivers though, 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.
> 
> Continue the transition to the new pattern with planes.
> 
> Signed-off-by: Maxime Ripard <mripard@kernel.org>
> ---
>  drivers/gpu/drm/drm_atomic_state_helper.c | 25 +++++++++++++++++++++++++
>  drivers/gpu/drm/drm_mode_config.c         | 21 ++++++++++++++++++++-
>  include/drm/drm_atomic_state_helper.h     |  2 ++
>  include/drm/drm_plane.h                   | 16 ++++++++++++++++
>  4 files changed, 63 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
> index 285efbf29520..50fe4eec41a8 100644
> --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> @@ -338,10 +338,35 @@ 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

drm_atomic_helper_colorop_create_state() states "Allocates and
initializes colorop atomic state", while here you document it as
"default hook for planes". Consistency would be good.

> + * @plane: plane object
> + *
> + * Initializes a pristine @drm_plane_state.

"Allocate and initialize ..."

> + *
> + * This is useful for drivers that don't subclass @drm_plane_state.
> + *
> + * RETURNS:
> + * Pointer to new plane state, or ERR_PTR on failure.
> + */
> +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_state_init(state, plane);
> +
> +	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 c33382a38191..10b7815cbe48 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;
> +
> +	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
> @@ -204,13 +220,16 @@ void drm_mode_config_reset(struct drm_device *dev)
>  	struct drm_connector_list_iter conn_iter;
>  
>  	drm_for_each_colorop(colorop, dev)
>  		drm_colorop_reset(colorop);
>  
> -	drm_for_each_plane(plane, dev)
> +	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 44e8850aae7f..df371b2eef3e 100644
> --- a/include/drm/drm_atomic_state_helper.h
> +++ b/include/drm/drm_atomic_state_helper.h
> @@ -53,10 +53,12 @@ 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_state_init(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 703ef4d1bbbc..886e219c4609 100644
> --- a/include/drm/drm_plane.h
> +++ b/include/drm/drm_plane.h
> @@ -386,10 +386,26 @@ 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

s/Allocates/Allocate/

based on the documentation of other callbacks, and the fact that
imperative style is the usual standard in kernel documentation.

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

> +	 * and returns 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, 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
  

Hi,

On Mon, May 04, 2026 at 07:52:29PM +0300, Laurent Pinchart wrote:
> On Fri, Apr 24, 2026 at 12:18:50PM +0200, 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 state, 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.
> > 
> > reset() also isn't fallible, which makes it harder to handle
> > initialization errors properly. This is only really relevant for some
> > drivers though, 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.
> > 
> > Continue the transition to the new pattern with planes.
> > 
> > Signed-off-by: Maxime Ripard <mripard@kernel.org>
> > ---
> >  drivers/gpu/drm/drm_atomic_state_helper.c | 25 +++++++++++++++++++++++++
> >  drivers/gpu/drm/drm_mode_config.c         | 21 ++++++++++++++++++++-
> >  include/drm/drm_atomic_state_helper.h     |  2 ++
> >  include/drm/drm_plane.h                   | 16 ++++++++++++++++
> >  4 files changed, 63 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
> > index 285efbf29520..50fe4eec41a8 100644
> > --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> > @@ -338,10 +338,35 @@ 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
> 
> drm_atomic_helper_colorop_create_state() states "Allocates and
> initializes colorop atomic state", while here you document it as
> "default hook for planes". Consistency would be good.

I don't think it's inconsistent?

colorops don't have a create_state callback, so the only function to
create it is defined as "Allocates and initializes colorop atomic
state". For planes, the hook is documented as "Allocates a pristine,
initialized, state for the plane object and returns it.", and here we
have the default implementation for that hook, which is documented as
such.

It all seems consistent to me?

Maxime