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authorLionel Landwerlin <lionel.g.landwerlin@intel.com>2020-01-14 15:19:28 +0300
committerChristian König <christian.koenig@amd.com>2020-01-20 16:22:21 +0300
commit77d1a6dbe8a4b878765816b82f3f2e7fff767c3f (patch)
tree22b2241d875d26a8aa41820ed4d1357adb2566c2 /drivers/gpu/drm/drm_syncobj.c
parentd1d511d516f72e0da2fea1e32a2dbf7b4f19b81f (diff)
downloadlinux-77d1a6dbe8a4b878765816b82f3f2e7fff767c3f.tar.xz
drm/syncobj: Add documentation for timeline syncobj
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> Reviewed-by: Christian König <christian.koenig@amd.com> Link: https://patchwork.freedesktop.org/patch/348578/ Cc: Christian Koenig <Christian.Koenig@amd.com> Cc: Jason Ekstrand <jason@jlekstrand.net> Cc: David(ChunMing) Zhou <David1.Zhou@amd.com> Signed-off-by: Christian König <christian.koenig@amd.com>
Diffstat (limited to 'drivers/gpu/drm/drm_syncobj.c')
-rw-r--r--drivers/gpu/drm/drm_syncobj.c87
1 files 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>