[PATCH 5/8] sync_file: add support for a semaphore object

[Dave Airlie]

From: Dave Airlie <airlied at redhat.com>

This object can be used to implement the Vulkan semaphores.

The object behaviour differs from fence, in that you can
replace the underlying fence, and you cannot merge semaphores.

Signed-off-by: Dave Airlie <airlied at redhat.com>
---
 drivers/dma-buf/sync_file.c    | 36 +++++++++++++++++++++++++++++++++++-
 include/linux/sync_file.h      |  2 ++
 include/uapi/linux/sync_file.h | 14 ++++++++++++++
 3 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index d84de67..a5b17c0 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -44,7 +44,7 @@ int sync_file_validate_type_flags(uint32_t type, uint32_t flags)
 {
 	if (flags)
 		return -EINVAL;
-	if (type != SYNC_FILE_TYPE_FENCE)
+	if (type != SYNC_FILE_TYPE_FENCE && type != SYNC_FILE_TYPE_SEMAPHORE)
 		return -EINVAL;
 	return 0;
 }
@@ -202,6 +202,38 @@ sync_file_get_fence_locked(struct sync_file *sync_file)
 					 sync_file_held(sync_file));
 }
 
+/**
+ * sync_file_replace_fence - replace the fence related to the sync_file
+ * @sync_file:	 sync file to replace fence in
+ * @fence: fence to replace with (or NULL for no fence).
+ * Returns previous fence.
+ */
+struct dma_fence *sync_file_replace_fence(struct sync_file *sync_file,
+					  struct dma_fence *fence)
+{
+	struct dma_fence *ret_fence = NULL;
+
+	if (sync_file->type != SYNC_FILE_TYPE_SEMAPHORE)
+		return NULL;
+
+	if (fence)
+		dma_fence_get(fence);
+
+	mutex_lock(&sync_file->lock);
+
+	ret_fence = sync_file_get_fence_locked(sync_file);
+	if (ret_fence) {
+		if (test_bit(POLL_ENABLED, &ret_fence->flags))
+			dma_fence_remove_callback(ret_fence, &sync_file->cb);
+	}
+
+	RCU_INIT_POINTER(sync_file->fence, fence);
+
+	mutex_unlock(&sync_file->lock);
+	return ret_fence;
+}
+EXPORT_SYMBOL(sync_file_replace_fence);
+
 static int sync_file_set_fence(struct sync_file *sync_file,
 			       struct dma_fence **fences, int num_fences)
 {
@@ -280,6 +312,8 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 
 	if (a->type != b->type)
 		return NULL;
+	if (a->type != SYNC_FILE_TYPE_FENCE)
+		return NULL;
 
 	if (!rcu_access_pointer(a->fence) ||
 	    !rcu_access_pointer(b->fence))
diff --git a/include/linux/sync_file.h b/include/linux/sync_file.h
index 4bf661b..245c7da 100644
--- a/include/linux/sync_file.h
+++ b/include/linux/sync_file.h
@@ -62,4 +62,6 @@ struct sync_file *sync_file_alloc(uint32_t type, uint32_t flags);
 struct sync_file *sync_file_create(struct dma_fence *fence, uint32_t type, uint32_t flags);
 struct dma_fence *sync_file_get_fence(int fd);
 struct sync_file *sync_file_fdget(int fd);
+struct dma_fence *sync_file_replace_fence(struct sync_file *sync_file,
+					  struct dma_fence *fence);
 #endif /* _LINUX_SYNC_H */
diff --git a/include/uapi/linux/sync_file.h b/include/uapi/linux/sync_file.h
index f439cda..5f266e0 100644
--- a/include/uapi/linux/sync_file.h
+++ b/include/uapi/linux/sync_file.h
@@ -80,6 +80,20 @@ struct sync_file_info {
 #define SYNC_FILE_TYPE_FENCE 0
 
 /**
+ * DOC: SYNC_FILE_TYPE_SEMAPHORE - semaphore sync file object
+ *
+ * This is a sync file that operates like a Vulkan semaphore.
+ * The object should just be imported/exported but not use the
+ * sync file ioctls (except info).
+ * This object can have it's backing fence replaced multiple times.
+ * Each signal operation assigns a backing fence.
+ * Each wait operation waits on the current fence, and removes it.
+ * These operations should happen via driver command submission interfaces.
+ * This is useful for shared vulkan semaphores.
+ */
+#define SYNC_FILE_TYPE_SEMAPHORE 1
+
+/**
  * struct sync_file_type - data returned from sync file type ioctl
  * @type:	sync_file type
  * @flags:	sync_file creation flags
-- 
2.9.3