[PATCH 01/12] dma-buf: add interface for user fence synchronization

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

This is a RFC/WIP patch which just adds the interface and lockdep
annotation without any actual implementation.

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/dma-buf/dma-resv.c | 18 ++++++++++++++++++
 include/linux/dma-resv.h   |  1 +
 2 files changed, 19 insertions(+)

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
index 6ddbeb5dfbf6..e0305424957b 100644
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -681,3 +681,21 @@ bool dma_resv_test_signaled_rcu(struct dma_resv *obj, bool test_all)
 	return ret;
 }
 EXPORT_SYMBOL_GPL(dma_resv_test_signaled_rcu);
+
+/**
+ * dma_resv_sync_user_fence - block for user fences to signal
+ *
+ * @obj: The DMA resv object with the user fence attached
+ *
+ * To make sure we have proper synchronization between accesses block for user
+ * fences before starting a dma_fence based operation on the buffer.
+ */
+int dma_resv_sync_user_fence(struct dma_resv *obj)
+{
+	might_fault();
+
+	/* TODO: Actually come up with an implementation for this! */
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dma_resv_sync_user_fence);
diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
index d44a77e8a7e3..c525a36be900 100644
--- a/include/linux/dma-resv.h
+++ b/include/linux/dma-resv.h
@@ -289,5 +289,6 @@ long dma_resv_wait_timeout_rcu(struct dma_resv *obj, bool wait_all, bool intr,
 			       unsigned long timeout);
 
 bool dma_resv_test_signaled_rcu(struct dma_resv *obj, bool test_all);
+int dma_resv_sync_user_fence(struct dma_resv *obj);
 
 #endif /* _LINUX_RESERVATION_H */
-- 
2.25.1

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