Re: [PATCH v2 08/20] drm/plane: Add new atomic_create_state callback

Thomas Zimmermann
2026-04-21T13:22:27Z

Hi

Am 20.03.26 um 17:27 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.
>
> 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.
>
> 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@kernel.org>
> ---
> drivers/gpu/drm/drm_atomic_state_helper.c | 44 +++++++++++++++++++++++++++++++
> drivers/gpu/drm/drm_mode_config.c | 21 ++++++++++++++-
> include/drm/drm_atomic_state_helper.h | 4 +++
> include/drm/drm_plane.h | 13 +++++++++
> 4 files changed, 81 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
> index 2548d6da13675f63304dc92423c5d225de0447a8..f4ce9d3573cbecf216904db54335e0cf84a01c39 100644
> --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> @@ -319,10 +319,29 @@ 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_state_init(state, plane);
> +}
> +EXPORT_SYMBOL(__drm_atomic_helper_plane_create_state);

Will this function have another purpuse?  Could we just call
_plane_state_init() directly from anywhere?

Best regards
Thomas

> +
> /**
> * 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
> @@ -338,10 +357,35 @@ 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
> + * @plane: plane object
> + *
> + * Initializes a pristine @drm_plane_state.
> + *
> + * 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_create_state(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 cba527571ca66d3aa6dc652c87e03a19815d1d41..09b8292195ba5eb5d96735aee5506407bd32ade3 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 44e8850aae7fd6390f4b58188a9c677b8389702f..6a3a2feb3dff1f2fbdf2a6e63d8d7317c7d6ead6 100644
> --- a/include/drm/drm_atomic_state_helper.h
> +++ b/include/drm/drm_atomic_state_helper.h
> @@ -53,10 +53,14 @@ 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);
> +void __drm_atomic_helper_plane_create_state(struct drm_plane *plane,
> + struct drm_plane_state *state);
> +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
>

--
--
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)