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

@@ -14,12 +14,14 @@
 #include <drm/drm_ioctl.h>
 #include <linux/delay.h>
 #include <linux/device.h>
+#include <linux/dma-fence.h>
+#include <linux/dma-fence-chain.h>
 #include <linux/dma-mapping.h>
 #include <linux/errname.h>
 #include <linux/slab.h>
 #include <linux/fs.h>
-#include <linux/io-pgtable.h>
 #include <linux/iosys-map.h>
+#include <linux/io-pgtable.h>
 #include <linux/ktime.h>
 #include <linux/lockdep.h>
 #include <linux/of.h>

rust/helpers.c

@@ -23,6 +23,8 @@
 #include <linux/bug.h>
 #include <linux/build_bug.h>
 #include <linux/device.h>
+#include <linux/dma-fence.h>
+#include <linux/dma-fence-chain.h>
 #include <linux/dma-mapping.h>
 #include <linux/err.h>
 #include <linux/errname.h>
@@ -436,6 +438,40 @@ int rust_helper_sg_dma_len(const struct scatterlist *sg)
 }
 EXPORT_SYMBOL_GPL(rust_helper_sg_dma_len);
 
+#ifdef CONFIG_DMA_SHARED_BUFFER
+
+void rust_helper_dma_fence_get(struct dma_fence *fence)
+{
+	dma_fence_get(fence);
+}
+EXPORT_SYMBOL_GPL(rust_helper_dma_fence_get);
+
+void rust_helper_dma_fence_put(struct dma_fence *fence)
+{
+	dma_fence_put(fence);
+}
+EXPORT_SYMBOL_GPL(rust_helper_dma_fence_put);
+
+struct dma_fence_chain *rust_helper_dma_fence_chain_alloc(void)
+{
+	return dma_fence_chain_alloc();
+}
+EXPORT_SYMBOL_GPL(rust_helper_dma_fence_chain_alloc);
+
+void rust_helper_dma_fence_chain_free(struct dma_fence_chain *chain)
+{
+	dma_fence_chain_free(chain);
+}
+EXPORT_SYMBOL_GPL(rust_helper_dma_fence_chain_free);
+
+void rust_helper_dma_fence_set_error(struct dma_fence *fence, int error)
+{
+	dma_fence_set_error(fence, error);
+}
+EXPORT_SYMBOL_GPL(rust_helper_dma_fence_set_error);
+
+#endif
+
 #ifdef CONFIG_DRM
 
 void rust_helper_drm_gem_object_get(struct drm_gem_object *obj)