We've added a set of new APIs to manipulate syncobjs holding timelines of dma_fence. This adds a bit of documentation about how this works.

v2: Small language nits (Lionel)

Signed-off-by: Lionel Landwerlin lionel.g.landwerlin@intel.com Cc: Christian Koenig Christian.Koenig@amd.com Cc: Jason Ekstrand jason@jlekstrand.net Cc: David(ChunMing) Zhou David1.Zhou@amd.com --- drivers/gpu/drm/drm_syncobj.c | 87 +++++++++++++++++++++++++++++------ 1 file changed, 74 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c index 669c93fe2500..42d46414f767 100644 --- a/drivers/gpu/drm/drm_syncobj.c +++ b/drivers/gpu/drm/drm_syncobj.c @@ -43,27 +43,66 @@ * - Signal a syncobj (set a trivially signaled fence) * - Wait for a syncobj's fence to appear and be signaled * + * The syncobj userspace API also provides operations to manipulate a syncobj + * in terms of a timeline of struct &dma_fence_chain rather than a single + * struct &dma_fence, through the following operations: + * + * - Signal a given point on the timeline + * - Wait for a given point to appear and/or be signaled + * - Import and export from/to a given point of a timeline + * * At it's core, a syncobj is simply a wrapper around a pointer to a struct * &dma_fence which may be NULL. * When a syncobj is first created, its pointer is either NULL or a pointer * to an already signaled fence depending on whether the * &DRM_SYNCOBJ_CREATE_SIGNALED flag is passed to * &DRM_IOCTL_SYNCOBJ_CREATE. - * When GPU work which signals a syncobj is enqueued in a DRM driver, - * the syncobj fence is replaced with a fence which will be signaled by the - * completion of that work. - * When GPU work which waits on a syncobj is enqueued in a DRM driver, the - * driver retrieves syncobj's current fence at the time the work is enqueued - * waits on that fence before submitting the work to hardware. - * If the syncobj's fence is NULL, the enqueue operation is expected to fail. - * All manipulation of the syncobjs's fence happens in terms of the current - * fence at the time the ioctl is called by userspace regardless of whether - * that operation is an immediate host-side operation (signal or reset) or - * or an operation which is enqueued in some driver queue. - * &DRM_IOCTL_SYNCOBJ_RESET and &DRM_IOCTL_SYNCOBJ_SIGNAL can be used to - * manipulate a syncobj from the host by resetting its pointer to NULL or + * + * If the syncobj is considered as a binary (its state is either signaled or + * unsignaled) primitive, when GPU work is enqueued in a DRM driver to signal + * the syncobj, the syncobj's fence is replaced with a fence which will be + * signaled by the completion of that work. + * If the syncobj is considered as a timeline primitive, when GPU work is + * enqueued in a DRM driver to signal the a given point of the syncobj, a new + * struct &dma_fence_chain pointing to the DRM driver's fence and also + * pointing to the previous fence that was in the syncobj. The new struct + * &dma_fence_chain fence replace the syncobj's fence and will be signaled by + * completion of the DRM driver's work and also any work associated with the + * fence previously in the syncobj. + * + * When GPU work which waits on a syncobj is enqueued in a DRM driver, at the + * time the work is enqueued, it waits on the syncobj's fence before + * submitting the work to hardware. That fence is either : + * + * - The syncobj's current fence if the syncobj is considered as a binary + * primitive. + * - The struct &dma_fence associated with a given point if the syncobj is + * considered as a timeline primitive. + * + * If the syncobj's fence is NULL or not present in the syncobj's timeline, + * the enqueue operation is expected to fail. + * + * With binary syncobj, all manipulation of the syncobjs's fence happens in + * terms of the current fence at the time the ioctl is called by userspace + * regardless of whether that operation is an immediate host-side operation + * (signal or reset) or or an operation which is enqueued in some driver + * queue. &DRM_IOCTL_SYNCOBJ_RESET and &DRM_IOCTL_SYNCOBJ_SIGNAL can be used + * to manipulate a syncobj from the host by resetting its pointer to NULL or * setting its pointer to a fence which is already signaled. * + * With a timeline syncobj, all manipulation of the synobj's fence happens in + * terms of a u64 value referring to point in the timeline. See + * dma_fence_chain_find_seqno() to see how a given point is found in the + * timeline. + * + * Note that applications should be careful to always use timeline set of + * ioctl() when dealing with syncobj considered as timeline. Using a binary + * set of ioctl() with a syncobj considered as timeline could result incorrect + * synchronization. The use of binary syncobj is supported through the + * timeline set of ioctl() by using a point value of 0, this will reproduce + * the behavior of the binary set of ioctl() (for example replace the + * syncobj's fence when signaling). + * * * Host-side wait on syncobjs * -------------------------- @@ -87,6 +126,16 @@ * synchronize between the two. * This requirement is inherited from the Vulkan fence API. * + * Similarly, &DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT takes an array of syncobj + * handles as well as an array of u64 points and does a host-side wait on all + * of syncobj fences at the given points simultaneously. + * + * &DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT also adds the ability to wait for a given + * fence to materialize on the timeline without waiting for the fence to be + * signaled by using the &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE flag. This + * requirement is inherited from the wait-before-signal behavior required by + * the Vulkan timeline semaphore API. + * * * Import/export of syncobjs * ------------------------- @@ -120,6 +169,18 @@ * Because sync files are immutable, resetting or signaling the syncobj * will not affect any sync files whose fences have been imported into the * syncobj. + * + * + * Import/export of timeline points in timeline syncobjs + * ----------------------------------------------------- + * + * &DRM_IOCTL_SYNCOBJ_TRANSFER provides a mechanism to transfer a struct + * &dma_fence_chain of a syncobj at a given u64 point to another u64 point + * into another syncobj. + * + * Note that if you want to transfer a struct &dma_fence_chain from a given + * point on a timeline syncobj from/into a binary syncobj, you can use the + * point 0 to mean take/replace the fence in the syncobj. */

#include <linux/anon_inodes.h>