Re: [PATCH 02/20] dma-buf: rework stub fence initialisation v2

[Tvrtko Ursulin]

On 31/10/2025 13:16, Christian König wrote:
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.koe...@amd.com>
---
  drivers/dma-buf/dma-fence.c | 32 +++++++++++++++-----------------
  1 file changed, 15 insertions(+), 17 deletions(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index cfa6ddcc1278..b229d96f551c 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);

Actually could you check if this could be demoted to static inline? It 
strikes me pointless to export a symbol for such a trivial wrapper.

Regards,

Tvrtko

  }
  EXPORT_SYMBOL(dma_fence_get_stub);