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

[Maxime Ripard]

Hi,

On Wed, Mar 11, 2026 at 09:13:18AM +0200, Tomi Valkeinen wrote:
> 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?

Yeah, this was supposed to be the latter. Thanks!
Maxime

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