rust: dma_fence: Add DMA Fence abstraction

DMA fences are the internal synchronization primitive used for DMA
operations like GPU rendering, video en/decoding, etc. Add an
abstraction to allow Rust drivers to interact with this subsystem.

Note: This uses a raw spinlock living next to the fence, since we do
not interact with it other than for initialization.
TODO: Expose this to the user at some point with a safe abstraction.

Signed-off-by: Asahi Lina <lina@asahilina.net>

Author: hoshinolina

rust/bindings/bindings_helper.h

@@ -51,6 +51,8 @@
 #include <linux/debugfs.h>
 #include <linux/device/faux.h>
 #include <linux/dma-direction.h>
+#include <linux/dma-fence.h>
+#include <linux/dma-fence-chain.h>
 #include <linux/dma-mapping.h>
 #include <linux/dma-resv.h>
 #include <linux/errname.h>

rust/helpers/dma-fence.c

@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/dma-fence.h>
+#include <linux/dma-fence-chain.h>
+
+#ifdef CONFIG_DMA_SHARED_BUFFER
+
+void rust_helper_dma_fence_get(struct dma_fence *fence)
+{
+	dma_fence_get(fence);
+}
+
+void rust_helper_dma_fence_put(struct dma_fence *fence)
+{
+	dma_fence_put(fence);
+}
+
+struct dma_fence_chain *rust_helper_dma_fence_chain_alloc(void)
+{
+	return dma_fence_chain_alloc();
+}
+
+void rust_helper_dma_fence_chain_free(struct dma_fence_chain *chain)
+{
+	dma_fence_chain_free(chain);
+}
+
+void rust_helper_dma_fence_set_error(struct dma_fence *fence, int error)
+{
+	dma_fence_set_error(fence, error);
+}
+
+#endif

rust/helpers/helpers.c

@@ -25,6 +25,7 @@
 #include "cred.c"
 #include "device.c"
 #include "dma.c"
+#include "dma-fence.c"
 #include "dma-mapping.c"
 #include "dma-resv.c"
 #include "drm.c"