Would one of you mind pushing? I don't have drm-misc commit bits. On Mon, Aug 12, 2019 at 9:22 AM Jason Ekstrand <ja...@jlekstrand.net> wrote:
> This patch only brings the syncobj documentation up-to-date for the > original form of syncobj. It does not contain any information about the > design of timeline syncobjs. > > v2: Incorporate feedback from Lionel and Christian: > - Mention actual ioctl and flag names > - Better language around reference counting > - Misc. language cleanups > > Signed-off-by: Jason Ekstrand <ja...@jlekstrand.net> > Reviewed-by: Lionel Landwerlin <lionel.g.landwer...@intel.com> > Acked-by: Christian König <christian.koe...@amd.com> > --- > drivers/gpu/drm/drm_syncobj.c | 98 +++++++++++++++++++++++++++++++---- > 1 file changed, 87 insertions(+), 11 deletions(-) > > diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c > index 1438dcb3ebb1..4b5c7b0ed714 100644 > --- a/drivers/gpu/drm/drm_syncobj.c > +++ b/drivers/gpu/drm/drm_syncobj.c > @@ -29,21 +29,97 @@ > /** > * DOC: Overview > * > - * DRM synchronisation objects (syncobj, see struct &drm_syncobj) are > - * persistent objects that contain an optional fence. The fence can be > updated > - * with a new fence, or be NULL. > + * DRM synchronisation objects (syncobj, see struct &drm_syncobj) provide > a > + * container for a synchronization primitive which can be used by > userspace > + * to explicitly synchronize GPU commands, can be shared between userspace > + * processes, and can be shared between different DRM drivers. > + * Their primary use-case is to implement Vulkan fences and semaphores. > + * The syncobj userspace API provides ioctls for several operations: > * > - * syncobj's can be waited upon, where it will wait for the underlying > - * fence. > + * - Creation and destruction of syncobjs > + * - Import and export of syncobjs to/from a syncobj file descriptor > + * - Import and export a syncobj's underlying fence to/from a sync file > + * - Reset a syncobj (set its fence to NULL) > + * - Signal a syncobj (set a trivially signaled fence) > + * - Wait for a syncobj's fence to appear and be signaled > * > - * syncobj's can be export to fd's and back, these fd's are opaque and > - * have no other use case, except passing the syncobj between processes. > + * 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 > + * setting its pointer to a fence which is already signaled. > * > - * Their primary use-case is to implement Vulkan fences and semaphores. > * > - * syncobj have a kref reference count, but also have an optional file. > - * The file is only created once the syncobj is exported. > - * The file takes a reference on the kref. > + * Host-side wait on syncobjs > + * -------------------------- > + * > + * &DRM_IOCTL_SYNCOBJ_WAIT takes an array of syncobj handles and does a > + * host-side wait on all of the syncobj fences simultaneously. > + * If &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_ALL is set, the wait ioctl will wait on > + * all of the syncobj fences to be signaled before it returns. > + * Otherwise, it returns once at least one syncobj fence has been signaled > + * and the index of a signaled fence is written back to the client. > + * > + * Unlike the enqueued GPU work dependencies which fail if they see a NULL > + * fence in a syncobj, if &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT is set, > + * the host-side wait will first wait for the syncobj to receive a > non-NULL > + * fence and then wait on that fence. > + * If &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT is not set and any one of > the > + * syncobjs in the array has a NULL fence, -EINVAL will be returned. > + * Assuming the syncobj starts off with a NULL fence, this allows a client > + * to do a host wait in one thread (or process) which waits on GPU work > + * submitted in another thread (or process) without having to manually > + * synchronize between the two. > + * This requirement is inherited from the Vulkan fence API. > + * > + * > + * Import/export of syncobjs > + * ------------------------- > + * > + * &DRM_IOCTL_SYNCOBJ_FD_TO_HANDLE and &DRM_IOCTL_SYNCOBJ_HANDLE_TO_FD > + * provide two mechanisms for import/export of syncobjs. > + * > + * The first lets the client import or export an entire syncobj to a file > + * descriptor. > + * These fd's are opaque and have no other use case, except passing the > + * syncobj between processes. > + * All exported file descriptors and any syncobj handles created as a > + * result of importing those file descriptors own a reference to the > + * same underlying struct &drm_syncobj and the syncobj can be used > + * persistently across all the processes with which it is shared. > + * The syncobj is freed only once the last reference is dropped. > + * Unlike dma-buf, importing a syncobj creates a new handle (with its own > + * reference) for every import instead of de-duplicating. > + * The primary use-case of this persistent import/export is for shared > + * Vulkan fences and semaphores. > + * > + * The second import/export mechanism, which is indicated by > + * &DRM_SYNCOBJ_FD_TO_HANDLE_FLAGS_IMPORT_SYNC_FILE or > + * &DRM_SYNCOBJ_HANDLE_TO_FD_FLAGS_EXPORT_SYNC_FILE lets the client > + * import/export the syncobj's current fence from/to a &sync_file. > + * When a syncobj is exported to a sync file, that sync file wraps the > + * sycnobj's fence at the time of export and any later signal or reset > + * operations on the syncobj will not affect the exported sync file. > + * When a sync file is imported into a syncobj, the syncobj's fence is set > + * to the fence wrapped by that sync file. > + * Because sync files are immutable, resetting or signaling the syncobj > + * will not affect any sync files whose fences have been imported into the > + * syncobj. > */ > > #include <linux/anon_inodes.h> > -- > 2.21.0 > >
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