Re: [PATCH v3 12/20] drm/crtc: Add new atomic_create_state callback

Laurent Pinchart
2026-05-04T17:29:11Z

On Fri, Apr 24, 2026 at 12:18:52PM +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 CRTCs.
>
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> Signed-off-by: Maxime Ripard <mripard@kernel.org>
> ---
> drivers/gpu/drm/drm_atomic_state_helper.c | 47 +++++++++++++++++++++++++++++++
> drivers/gpu/drm/drm_mode_config.c | 21 +++++++++++++-
> include/drm/drm_atomic_state_helper.h | 4 +++
> include/drm/drm_crtc.h | 16 +++++++++++
> 4 files changed, 87 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
> index 9cd8550cabb7..b7da134c8c50 100644
> --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> @@ -103,10 +103,32 @@ __drm_atomic_helper_crtc_reset(struct drm_crtc *crtc,
>
> crtc->state = crtc_state;
> }
> EXPORT_SYMBOL(__drm_atomic_helper_crtc_reset);
>
> +/**
> + * __drm_atomic_helper_crtc_create_state - initializes crtc state

"Initialize a CRTC state"

The name of the function is misleading ("*_create_*" while you state it
performs initialization).

> + * @crtc: crtc 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_crtc_state.
> + */
> +void __drm_atomic_helper_crtc_create_state(struct drm_crtc *crtc,
> + struct drm_crtc_state *state)
> +{
> + __drm_atomic_helper_crtc_state_init(state, crtc);
> +
> + if (drm_dev_has_vblank(crtc->dev))
> + drm_crtc_vblank_reset(crtc);

This is confusing to me (at least before reading the rest of the
series), and itn't mentioned in the function documentation or in the
commit message.

Furthermore, __drm_atomic_helper_crtc_create_state() is later used in
tidss_crtc_create_state(), which is the
drm_crtc_funcs.atomic_create_state() implementation of the tidss driver.
The atomic_create_state documentation states that "This callback must
have no side effect", and drm_crtc_vblank_reset() has side effects.

> +}
> +EXPORT_SYMBOL(__drm_atomic_helper_crtc_create_state);
> +
> /**
> * drm_atomic_helper_crtc_reset - default &drm_crtc_funcs.reset hook for CRTCs
> * @crtc: drm CRTC
> *
> * Resets the atomic state for @crtc by freeing the state pointer (which might
> @@ -122,10 +144,35 @@ void drm_atomic_helper_crtc_reset(struct drm_crtc *crtc)
>
> __drm_atomic_helper_crtc_reset(crtc, crtc_state);
> }
> EXPORT_SYMBOL(drm_atomic_helper_crtc_reset);
>
> +/**
> + * drm_atomic_helper_crtc_create_state - default &drm_crtc_funcs.atomic_create_state hook for crtcs

Same comment as in patch 10/20.

> + * @crtc: crtc object
> + *
> + * Initializes a pristine @drm_crtc_state.

"Allocate and initialize ..."

> + *
> + * This is useful for drivers that don't subclass @drm_crtc_state.
> + *
> + * RETURNS:
> + * Pointer to new crtc state, or ERR_PTR on failure.
> + */
> +struct drm_crtc_state *drm_atomic_helper_crtc_create_state(struct drm_crtc *crtc)
> +{
> + struct drm_crtc_state *state;
> +
> + state = kzalloc_obj(*state);
> + if (!state)
> + return ERR_PTR(-ENOMEM);
> +
> + __drm_atomic_helper_crtc_create_state(crtc, state);
> +
> + return state;
> +}
> +EXPORT_SYMBOL(drm_atomic_helper_crtc_create_state);
> +
> /**
> * __drm_atomic_helper_crtc_duplicate_state - copy atomic CRTC state
> * @crtc: CRTC object
> * @state: atomic CRTC state
> *
> diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> index 10b7815cbe48..182d9a8104e7 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -196,10 +196,26 @@ static int drm_mode_config_plane_create_state(struct drm_plane *plane)
> plane->state = plane_state;
>
> return 0;
> }
>
> +static int drm_mode_config_crtc_create_state(struct drm_crtc *crtc)
> +{
> + struct drm_crtc_state *crtc_state;
> +
> + if (!crtc->funcs->atomic_create_state)
> + return 0;
> +
> + crtc_state = crtc->funcs->atomic_create_state(crtc);
> + if (IS_ERR(crtc_state))
> + return PTR_ERR(crtc_state);
> +
> + crtc->state = crtc_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
> @@ -227,13 +243,16 @@ void drm_mode_config_reset(struct drm_device *dev)
> plane->funcs->reset(plane);
> else if (plane->funcs->atomic_create_state)
> drm_mode_config_plane_create_state(plane);
> }
>
> - drm_for_each_crtc(crtc, dev)
> + drm_for_each_crtc(crtc, dev) {
> if (crtc->funcs->reset)
> crtc->funcs->reset(crtc);
> + else if (crtc->funcs->atomic_create_state)
> + drm_mode_config_crtc_create_state(crtc);
> + }
>
> drm_for_each_encoder(encoder, dev)
> if (encoder->funcs && encoder->funcs->reset)
> encoder->funcs->reset(encoder);
>
> diff --git a/include/drm/drm_atomic_state_helper.h b/include/drm/drm_atomic_state_helper.h
> index e7fbbfdc5d69..129762b99de6 100644
> --- a/include/drm/drm_atomic_state_helper.h
> +++ b/include/drm/drm_atomic_state_helper.h
> @@ -43,10 +43,14 @@ struct drm_device;
> void __drm_atomic_helper_crtc_state_init(struct drm_crtc_state *state,
> struct drm_crtc *crtc);
> void __drm_atomic_helper_crtc_reset(struct drm_crtc *crtc,
> struct drm_crtc_state *state);
> void drm_atomic_helper_crtc_reset(struct drm_crtc *crtc);
> +void __drm_atomic_helper_crtc_create_state(struct drm_crtc *crtc,
> + struct drm_crtc_state *state);
> +struct drm_crtc_state *
> +drm_atomic_helper_crtc_create_state(struct drm_crtc *crtc);
> void __drm_atomic_helper_crtc_duplicate_state(struct drm_crtc *crtc,
> struct drm_crtc_state *state);
> 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);
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index 312fc1e745d2..41ea6eadf36f 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -636,10 +636,26 @@ struct drm_crtc_funcs {
> * 0 on success or a negative error code on failure.
> */
> int (*set_property)(struct drm_crtc *crtc,
> struct drm_property *property, uint64_t val);
>
> + /**
> + * @atomic_create_state:
> + *
> + * Allocates a pristine, initialized, state for the CRTC object

s/Allocates/Allocate/

> + * 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, CRTC state instance or an error pointer
> + * on failure.
> + */
> + struct drm_crtc_state *(*atomic_create_state)(struct drm_crtc *crtc);
> +
> /**
> * @atomic_duplicate_state:
> *
> * Duplicate the current atomic state for this CRTC and return it.
> * The core and helpers guarantee that any atomic state duplicated with

--
Regards,

Laurent Pinchart