[v3,12/20] drm/crtc: 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 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(-)
  

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
  

Hi,

On Mon, May 04, 2026 at 08:28:58PM +0300, Laurent Pinchart wrote:
> 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"

Good catch, thanks.

> 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.

That's a good point. I've dropped that function entirely and moved the
drm_crtc_vblank_reset() call in drm_mode_config_crtc_create_state().

Maxime