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

Maxime Ripard
2026-04-23T10:54:41Z

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On Tue, Apr 21, 2026 at 03:22:22PM +0200, Thomas Zimmermann wrote:
> 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?

Yeah, I guess that makes sense. I'll drop that patch and the similar ones.

Thanks!
Maxime

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