drm/crtc: Add new atomic_create_state callback

Commit 47b5ac7daa ("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>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patch.msgid.link/20260526-drm-mode-config-init-v6-12-852346394200@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

drivers/gpu/drm/drm_atomic_state_helper.c

@@ -124,6 +124,31 @@ void drm_atomic_helper_crtc_reset(struct drm_crtc *crtc)
 }
 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
+ *
+ * Allocates and  initializes 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_state_init(state, crtc);
+
+	return state;
+}
+EXPORT_SYMBOL(drm_atomic_helper_crtc_create_state);
+
 /**
  * __drm_atomic_helper_crtc_duplicate_state - copy atomic CRTC state
  * @crtc: CRTC object

drivers/gpu/drm/drm_mode_config.c

@@ -208,6 +208,35 @@ static int drm_mode_config_plane_reset_with_create_state(struct drm_plane *plane
 	return drm_mode_config_plane_create_state(plane);
 }
 
+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);
+
+	if (drm_dev_has_vblank(crtc->dev))
+		drm_crtc_vblank_reset(crtc);
+
+	crtc->state = crtc_state;
+
+	return 0;
+}
+
+static int drm_mode_config_crtc_reset_with_create_state(struct drm_crtc *crtc)
+{
+	if (crtc->state) {
+		crtc->funcs->atomic_destroy_state(crtc, crtc->state);
+		crtc->state = NULL;
+	}
+
+	return drm_mode_config_crtc_create_state(crtc);
+}
+
 /**
  * drm_mode_config_reset - call ->reset callbacks
  * @dev: drm device
@@ -239,9 +268,12 @@ void drm_mode_config_reset(struct drm_device *dev)
 			drm_mode_config_plane_reset_with_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_reset_with_create_state(crtc);
+	}
 
 	drm_for_each_encoder(encoder, dev)
 		if (encoder->funcs && encoder->funcs->reset)

include/drm/drm_atomic_state_helper.h

@@ -45,6 +45,8 @@ void __drm_atomic_helper_crtc_state_init(struct drm_crtc_state *state,
 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);
+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 *

include/drm/drm_crtc.h

@@ -638,6 +638,22 @@ struct drm_crtc_funcs {
 	int (*set_property)(struct drm_crtc *crtc,
 			    struct drm_property *property, uint64_t val);
 
+	/**
+	 * @atomic_create_state:
+	 *
+	 * Allocate a pristine, initialized, state for the CRTC object
+	 * and return 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:
 	 *