Hi,
On Wed, Oct 15, 2025 at 06:03:14PM +0200, Boris Brezillon wrote:
> Prepare things for standardizing synchronization around CPU accesses
> of GEM buffers. This will be used to provide default
> drm_gem_dmabuf_{begin,end}_cpu_access() implementations, and provide
> a way for drivers to add their own ioctls to synchronize CPU
> writes/reads when they can't do it directly from userland.
>
> v2:
> - New commit
>
> v3:
> - No changes
>
> v4:
> - Add Steve's R-b
>
> Signed-off-by: Boris Brezillon <[email protected]>
> Reviewed-by: Steven Price <[email protected]>
> ---
> drivers/gpu/drm/drm_gem.c | 10 +++++++++
> include/drm/drm_gem.h | 45 +++++++++++++++++++++++++++++++++++++++
> 2 files changed, 55 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index a1a9c828938b..a1431e4f2404 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -1333,6 +1333,16 @@ void drm_gem_vunmap(struct drm_gem_object *obj, struct
> iosys_map *map)
> }
> EXPORT_SYMBOL(drm_gem_vunmap);
>
> +int drm_gem_sync(struct drm_gem_object *obj, size_t offset, size_t size,
> + enum drm_gem_object_access_flags access)
> +{
> + if (obj->funcs->sync)
> + return obj->funcs->sync(obj, offset, size, access);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL(drm_gem_sync);
> +
> /**
> * drm_gem_lock_reservations - Sets up the ww context and acquires
> * the lock on an array of GEM objects.
> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> index 8d48d2af2649..1c33e59ab305 100644
> --- a/include/drm/drm_gem.h
> +++ b/include/drm/drm_gem.h
> @@ -66,6 +66,33 @@ enum drm_gem_object_status {
> DRM_GEM_OBJECT_ACTIVE = BIT(2),
> };
>
> +/**
> + * enum drm_gem_object_status - bitmask describing GEM access types to
> prepare for
Treating an enum as a bitmask is a bit weird to me. I'd say either have
a bitmask with BIT(enum values), or no enum at all.
> + */
> +enum drm_gem_object_access_flags {
> + /** @DRM_GEM_OBJECT_CPU_ACCESS: Prepare for a CPU access. */
> + DRM_GEM_OBJECT_CPU_ACCESS = 0,
> +
> + /** @DRM_GEM_OBJECT_DEV_ACCESS: Prepare for a device access. */
> + DRM_GEM_OBJECT_DEV_ACCESS = BIT(0),
> +
> + /** @DRM_GEM_OBJECT_ACCESSOR_MASK: Mask used to check the entity doing
> the access. */
> + DRM_GEM_OBJECT_ACCESSOR_MASK = BIT(0),
Do we really want to have to variants with the same discriminant? If so,
we should document why it's something we want.
> + /** @DRM_GEM_OBJECT_READ_ACCESS: Prepare for read-only accesses. */
> + DRM_GEM_OBJECT_READ_ACCESS = BIT(1),
> +
> + /** @DRM_GEM_OBJECT_WRITE_ACCESS: Prepare for write-only accesses. */
> + DRM_GEM_OBJECT_WRITE_ACCESS = BIT(2),
> +
> + /** @DRM_GEM_OBJECT_RW_ACCESS: Prepare for a read/write accesses. */
> + DRM_GEM_OBJECT_RW_ACCESS = DRM_GEM_OBJECT_READ_ACCESS |
> + DRM_GEM_OBJECT_WRITE_ACCESS,
> +
> + /** @DRM_GEM_OBJECT_ACCESS_TYPE_MASK: Mask used to check the access
> type. */
> + DRM_GEM_OBJECT_ACCESS_TYPE_MASK = DRM_GEM_OBJECT_RW_ACCESS,
Same thing.
Or is it that you encode both the direction and access type, and have a
mask to isolate each?
If so, we should really move it out from an enum into defines, or treat each
separately like dma_sync_does.
Maxime
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