Re: [PATCH v3 09/11] drm/atomic-uapi: Add DRM_MODE_ATOMIC_RESET flag

[Thomas Zimmermann <tzimmermann@suse.de>]

Am 08.09.26 um 16:35 schrieb Maxime Ripard:
> From: Sebastian Wick <sebastian.wick@redhat.com>
>
> Userspace currently has no atomic way to reset all KMS object states
> to their defaults. To bring a display pipeline to a known state, a
> compositor must explicitly set every property on every object, which
> requires tracking which properties exist and what their defaults are.
>
> Introduce DRM_MODE_ATOMIC_RESET (0x0800) which, when passed to the
> atomic ioctl, fills the commit with default states for all KMS
> objects before applying the properties supplied in the request.
> Properties not explicitly included in the commit remain at their
> defaults (CRTCs inactive, planes disabled, connectors unbound, and
> so on).
>
> The flag cannot be combined with DRM_MODE_PAGE_FLIP_ASYNC, since a
> full state reset is incompatible with an async flip.
>
> Signed-off-by: Sebastian Wick <sebastian.wick@redhat.com>
> Co-developed-by: Maxime Ripard <mripard@kernel.org>
> Signed-off-by: Maxime Ripard <mripard@kernel.org>

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>


> ---
>   drivers/gpu/drm/drm_atomic.c      |  3 +++
>   drivers/gpu/drm/drm_atomic_uapi.c | 13 +++++++++++++
>   drivers/gpu/drm/drm_ioctl.c       |  3 +++
>   include/uapi/drm/drm.h            | 10 ++++++++++
>   include/uapi/drm/drm_mode.h       | 14 +++++++++++++-
>   5 files changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 4c15757308d6..d5b3a7d99239 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -1625,10 +1625,13 @@ EXPORT_SYMBOL(drm_atomic_get_new_bridge_state);
>    * the current state.
>    *
>    * Color operations are not checked because they always use
>    * drm_atomic_helper_colorop_create_state() and do not have a per-driver hook.
>    *
> + * This is used to report the %DRM_CAP_ATOMIC_RESET capability to userspace,
> + * and as a precondition in drm_atomic_commit_fill_with_defaults().
> + *
>    * Returns:
>    * True if all objects implement atomic_create_state, false otherwise.
>    */
>   bool drm_atomic_can_create_state(struct drm_device *dev)
>   {
> diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
> index d52504d823bc..fe794a65a727 100644
> --- a/drivers/gpu/drm/drm_atomic_uapi.c
> +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> @@ -1665,10 +1665,17 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
>   		drm_dbg_atomic(dev,
>   			       "commit failed: page-flip event requested with test-only commit\n");
>   		return -EINVAL;
>   	}
>   
> +	if ((arg->flags & DRM_MODE_ATOMIC_RESET) &&
> +			(arg->flags & DRM_MODE_PAGE_FLIP_ASYNC)) {
> +		drm_dbg_atomic(dev,
> +			       "commit failed: reset cannot be combined with async flip\n");
> +		return -EINVAL;
> +	}
> +
>   	state = drm_atomic_commit_alloc(dev);
>   	if (!state)
>   		return -ENOMEM;
>   
>   	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
> @@ -1680,10 +1687,16 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
>   	copied_objs = 0;
>   	copied_props = 0;
>   	fence_state = NULL;
>   	num_fences = 0;
>   
> +	if (arg->flags & DRM_MODE_ATOMIC_RESET) {
> +		ret = drm_atomic_commit_fill_with_defaults(state);
> +		if (ret)
> +			goto out;
> +	}
> +
>   	for (i = 0; i < arg->count_objs; i++) {
>   		uint32_t obj_id, count_props;
>   		struct drm_mode_object *obj;
>   
>   		if (get_user(obj_id, objs_ptr + copied_objs)) {
> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
> index 0dbf04d4aa9e..f13bb7c490c4 100644
> --- a/drivers/gpu/drm/drm_ioctl.c
> +++ b/drivers/gpu/drm/drm_ioctl.c
> @@ -303,10 +303,13 @@ static int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_
>   		break;
>   	case DRM_CAP_ATOMIC_ASYNC_PAGE_FLIP:
>   		req->value = drm_core_check_feature(dev, DRIVER_ATOMIC) &&
>   			     dev->mode_config.async_page_flip;
>   		break;
> +	case DRM_CAP_ATOMIC_RESET:
> +		req->value = drm_atomic_can_create_state(dev);
> +		break;
>   	default:
>   		return -EINVAL;
>   	}
>   	return 0;
>   }
> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> index bc7ef7684099..b6e2f2edd122 100644
> --- a/include/uapi/drm/drm.h
> +++ b/include/uapi/drm/drm.h
> @@ -793,10 +793,20 @@ struct drm_gem_change_handle {
>    * If set to 1, the driver supports &DRM_MODE_PAGE_FLIP_ASYNC for atomic
>    * commits.
>    */
>   #define DRM_CAP_ATOMIC_ASYNC_PAGE_FLIP	0x15
>   
> +/**
> + * DRM_CAP_ATOMIC_RESET
> + *
> + * If set to 1, the driver supports the &DRM_MODE_ATOMIC_RESET flag in
> + * &DRM_IOCTL_MODE_ATOMIC commits. When supported, userspace can pass that
> + * flag to reset all KMS object states to their defaults before applying
> + * property changes.
> + */
> +#define DRM_CAP_ATOMIC_RESET	0x16
> +
>   /* DRM_IOCTL_GET_CAP ioctl argument type */
>   struct drm_get_cap {
>   	__u64 capability;
>   	__u64 value;
>   };
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index ed1a660a3dfd..32eb3f650d7a 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -1326,10 +1326,21 @@ struct drm_mode_destroy_dumb {
>    * To the best of the driver's knowledge, visual artifacts are guaranteed to
>    * not appear when this flag is not set. Some sinks might display visual
>    * artifacts outside of the driver's control.
>    */
>   #define DRM_MODE_ATOMIC_ALLOW_MODESET 0x0400
> +/**
> + * DRM_MODE_ATOMIC_RESET
> + *
> + * Reset all KMS object states (CRTCs, planes, connectors, color operations)
> + * to their default values before applying the properties in this commit.
> + * Properties not explicitly included in the commit will remain at their
> + * defaults (CRTCs inactive, planes disabled, connectors unbound, etc.).
> + *
> + * This flag cannot be combined with &DRM_MODE_PAGE_FLIP_ASYNC.
> + */
> +#define DRM_MODE_ATOMIC_RESET 0x0800
>   
>   /**
>    * DRM_MODE_ATOMIC_FLAGS
>    *
>    * Bitfield of flags accepted by the &DRM_IOCTL_MODE_ATOMIC IOCTL in
> @@ -1338,11 +1349,12 @@ struct drm_mode_destroy_dumb {
>   #define DRM_MODE_ATOMIC_FLAGS (\
>   		DRM_MODE_PAGE_FLIP_EVENT |\
>   		DRM_MODE_PAGE_FLIP_ASYNC |\
>   		DRM_MODE_ATOMIC_TEST_ONLY |\
>   		DRM_MODE_ATOMIC_NONBLOCK |\
> -		DRM_MODE_ATOMIC_ALLOW_MODESET)
> +		DRM_MODE_ATOMIC_ALLOW_MODESET |\
> +		DRM_MODE_ATOMIC_RESET)
>   
>   struct drm_mode_atomic {
>   	__u32 flags;
>   	__u32 count_objs;
>   	__u64 objs_ptr;
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, (HRB 36809, AG Nürnberg)