dma-buf: rework stub fence initialisation v2

Instead of doing this on the first call of the function just initialize
the stub fence during kernel load.

This has the clear advantage of lower overhead and also doesn't rely on
the ops to not be NULL any more.

v2: use correct signal function

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Link: https://lore.kernel.org/r/20251031134442.113648-3-christian.koenig@amd.com

1 files changed, 15 insertions, 17 deletions

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 3f78c56b58dc..35e241041c10 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -121,29 +121,27 @@ static const struct dma_fence_ops dma_fence_stub_ops = {
 	.get_timeline_name = dma_fence_stub_get_name,
 };
 
+static int __init dma_fence_init_stub(void)
+{
+	dma_fence_init(&dma_fence_stub, &dma_fence_stub_ops,
+		       &dma_fence_stub_lock, 0, 0);
+
+	set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
+		&dma_fence_stub.flags);
+
+	dma_fence_signal(&dma_fence_stub);
+	return 0;
+}
+subsys_initcall(dma_fence_init_stub);
+
 /**
  * dma_fence_get_stub - return a signaled fence
  *
- * Return a stub fence which is already signaled. The fence's
- * timestamp corresponds to the first time after boot this
- * function is called.
+ * Return a stub fence which is already signaled. The fence's timestamp
+ * corresponds to the initialisation time of the linux kernel.
  */
 struct dma_fence *dma_fence_get_stub(void)
 {
-	spin_lock(&dma_fence_stub_lock);
-	if (!dma_fence_stub.ops) {
-		dma_fence_init(&dma_fence_stub,
-			       &dma_fence_stub_ops,
-			       &dma_fence_stub_lock,
-			       0, 0);
-
-		set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
-			&dma_fence_stub.flags);
-
-		dma_fence_signal_locked(&dma_fence_stub);
-	}
-	spin_unlock(&dma_fence_stub_lock);
-
 	return dma_fence_get(&dma_fence_stub);
 }
 EXPORT_SYMBOL(dma_fence_get_stub);