[PATCH 1/3] dma-buf/sync_file: only enable fence signalling during wait

[Gustavo Padovan <gustavo@padovan.org>]

From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

Signalling doesn't need to be enabled at sync_file creation, it is only
required if userspace waiting the fence to signal through poll().

Thus we delay fence_add_callback() until poll is called. It only adds the
callback the first time poll() is called. This avoid re-adding the same
callback multiple times.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
 drivers/dma-buf/sync_file.c | 36 +++++++++++++++++++++++-------------
 include/linux/fence.h       | 12 ++++++++++++
 2 files changed, 35 insertions(+), 13 deletions(-)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 00e9186..59f3445 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -91,9 +91,7 @@ struct sync_file *sync_file_create(struct fence *fence)
 
 	sync_file->cbs[0].fence = fence;
 	sync_file->cbs[0].sync_file = sync_file;
-	if (fence_add_callback(fence, &sync_file->cbs[0].cb,
-			       fence_check_cb_func))
-		atomic_dec(&sync_file->status);
+	INIT_LIST_HEAD(&sync_file->cbs[0].cb.node);
 
 	sync_file_debug_add(sync_file);
 	return sync_file;
@@ -130,8 +128,7 @@ static void sync_file_add_pt(struct sync_file *sync_file, int *i,
 	sync_file->cbs[*i].fence = fence;
 	sync_file->cbs[*i].sync_file = sync_file;
 
-	if (!fence_add_callback(fence, &sync_file->cbs[*i].cb,
-				fence_check_cb_func)) {
+	if (!fence_is_signaled(fence)) {
 		fence_get(fence);
 		(*i)++;
 	}
@@ -212,11 +209,8 @@ static void sync_file_free(struct kref *kref)
 						     kref);
 	int i;
 
-	for (i = 0; i < sync_file->num_fences; ++i) {
-		fence_remove_callback(sync_file->cbs[i].fence,
-				      &sync_file->cbs[i].cb);
+	for (i = 0; i < sync_file->num_fences; ++i)
 		fence_put(sync_file->cbs[i].fence);
-	}
 
 	sync_file_debug_remove(sync_file);
 	kfree(sync_file);
@@ -233,17 +227,33 @@ static int sync_file_release(struct inode *inode, struct file *file)
 static unsigned int sync_file_poll(struct file *file, poll_table *wait)
 {
 	struct sync_file *sync_file = file->private_data;
-	int status;
+	int status, i;
 
 	poll_wait(file, &sync_file->wq, wait);
 
+	for (i = 0 ; i < sync_file->num_fences ; i++) {
+		if (fence_is_enabled(sync_file->cbs[i].fence))
+			continue;
+
+		if (fence_add_callback(sync_file->cbs[i].fence,
+				       &sync_file->cbs[i].cb,
+				       fence_check_cb_func))
+			atomic_dec(&sync_file->status);
+	}
+
 	status = atomic_read(&sync_file->status);
 
-	if (!status)
-		return POLLIN;
+	if (status > 0)
+		return 0;
+
+	for (i = 0 ; i < sync_file->num_fences ; i++)
+		fence_remove_callback(sync_file->cbs[i].fence,
+				      &sync_file->cbs[i].cb);
+
 	if (status < 0)
 		return POLLERR;
-	return 0;
+
+	return POLLIN;
 }
 
 static long sync_file_ioctl_merge(struct sync_file *sync_file,
diff --git a/include/linux/fence.h b/include/linux/fence.h
index 523ea3f..95a70b2 100644
--- a/include/linux/fence.h
+++ b/include/linux/fence.h
@@ -283,6 +283,18 @@ fence_is_signaled(struct fence *fence)
 }
 
 /**
+ * fence_is_enabled - return an indication if signalling is enabled
+ * @fence:	[in]	the fence to check
+ *
+ * Returns true if signalling was already enabled, false if not.
+ */
+static inline bool
+fence_is_enabled(struct fence *fence)
+{
+	return test_bit(FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags);
+}
+
+/**
  * fence_is_later - return if f1 is chronologically later than f2
  * @f1:	[in]	the first fence from the same context
  * @f2:	[in]	the second fence from the same context
-- 
2.5.5