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

Maxime Ripard
2026-04-24T10:19:48Z

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
+ * @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);
+}
+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
+ * @crtc: crtc object
+ *
+ * Initializes a pristine @drm_crtc_state.
+ *
+ * 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
+ * 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

--
2.53.0