[RFC,3/3] dma-bikeshed-fence: Hardware dma-buf implementation of fencing

diff --git a/drivers/base/Makefile b/drivers/base/Makefile
index 6e9f217..1e7723b 100644
--- a/drivers/base/Makefile
+++ b/drivers/base/Makefile
@@ -10,7 +10,7 @@  obj-$(CONFIG_CMA) += dma-contiguous.o
 obj-y			+= power/
 obj-$(CONFIG_HAS_DMA)	+= dma-mapping.o
 obj-$(CONFIG_HAVE_GENERIC_DMA_COHERENT) += dma-coherent.o
-obj-$(CONFIG_DMA_SHARED_BUFFER) += dma-buf.o dma-fence.o
+obj-$(CONFIG_DMA_SHARED_BUFFER) += dma-buf.o dma-fence.o dma-bikeshed-fence.o
 obj-$(CONFIG_ISA)	+= isa.o
 obj-$(CONFIG_FW_LOADER)	+= firmware_class.o
 obj-$(CONFIG_NUMA)	+= node.o
diff --git a/drivers/base/dma-bikeshed-fence.c b/drivers/base/dma-bikeshed-fence.c
new file mode 100644
index 0000000..fa063e8
--- /dev/null
+++ b/drivers/base/dma-bikeshed-fence.c
@@ -0,0 +1,44 @@ 
+/*
+ * dma-fence implementation that supports hw synchronization via hw
+ * read/write of memory semaphore
+ *
+ * Copyright (C) 2012 Texas Instruments
+ * Author: Rob Clark <rob.clark@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/export.h>
+#include <linux/slab.h>
+#include <linux/dma-bikeshed-fence.h>
+
+static int enable_signaling(struct dma_fence *fence)
+{
+	struct dma_bikeshed_fence *bikeshed_fence = to_bikeshed_fence(fence);
+	return bikeshed_fence->enable_signaling(bikeshed_fence);
+}
+
+static void bikeshed_release(struct dma_fence *fence)
+{
+	struct dma_bikeshed_fence *f = to_bikeshed_fence(fence);
+
+	if (f->release)
+		f->release(f);
+	dma_buf_put(f->sync_buf);
+}
+
+struct dma_fence_ops dma_bikeshed_fence_ops = {
+	.enable_signaling = enable_signaling,
+	.release = bikeshed_release
+};
+EXPORT_SYMBOL_GPL(dma_bikeshed_fence_ops);
diff --git a/include/linux/dma-bikeshed-fence.h b/include/linux/dma-bikeshed-fence.h
new file mode 100644
index 0000000..4f19801
--- /dev/null
+++ b/include/linux/dma-bikeshed-fence.h
@@ -0,0 +1,92 @@ 
+/*
+ * dma-fence implementation that supports hw synchronization via hw
+ * read/write of memory semaphore
+ *
+ * Copyright (C) 2012 Texas Instruments
+ * Author: Rob Clark <rob.clark@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __DMA_BIKESHED_FENCE_H__
+#define __DMA_BIKESHED_FENCE_H__
+
+#include <linux/types.h>
+#include <linux/dma-fence.h>
+#include <linux/dma-buf.h>
+
+struct dma_bikeshed_fence {
+	struct dma_fence base;
+
+	struct dma_buf *sync_buf;
+	uint32_t seqno_ofs;
+	uint32_t seqno;
+
+	int (*enable_signaling)(struct dma_bikeshed_fence *fence);
+	void (*release)(struct dma_bikeshed_fence *fence);
+};
+
+/*
+ * TODO does it make sense to be able to enable dma-fence without dma-buf,
+ * or visa versa?
+ */
+#ifdef CONFIG_DMA_SHARED_BUFFER
+
+extern struct dma_fence_ops dma_bikeshed_fence_ops;
+
+static inline bool is_bikeshed_fence(struct dma_fence *fence)
+{
+	return fence->ops == &dma_bikeshed_fence_ops;
+}
+
+static inline struct dma_bikeshed_fence *to_bikeshed_fence(struct dma_fence *fence)
+{
+	if (WARN_ON(!is_bikeshed_fence(fence)))
+		return NULL;
+	return container_of(fence, struct dma_bikeshed_fence, base);
+}
+
+/**
+ * dma_bikeshed_fence_init - Initialize a fence
+ *
+ * @fence: dma_bikeshed_fence to initialize
+ * @sync_buf: buffer containing the memory location to signal on
+ * @seqno_ofs: the offset within @sync_buf
+ * @seqno: the sequence # to signal on
+ * @priv: value of priv member
+ * @enable_signaling: callback which is called when some other device is
+ *    waiting for sw notification of fence
+ * @release: callback called during destruction before object is freed.
+ */
+static inline void dma_bikeshed_fence_init(struct dma_bikeshed_fence *fence,
+		struct dma_buf *sync_buf,
+		uint32_t seqno_ofs, uint32_t seqno, void *priv,
+		int (*enable_signaling)(struct dma_bikeshed_fence *fence),
+		void (*release)(struct dma_bikeshed_fence *fence))
+{
+	BUG_ON(!fence || !sync_buf || !enable_signaling);
+
+	__dma_fence_init(&fence->base, &dma_bikeshed_fence_ops, priv);
+
+	get_dma_buf(sync_buf);
+	fence->sync_buf = sync_buf;
+	fence->seqno_ofs = seqno_ofs;
+	fence->seqno = seqno;
+	fence->enable_signaling = enable_signaling;
+}
+
+#else
+// TODO
+#endif /* CONFIG_DMA_SHARED_BUFFER */
+
+#endif /* __DMA_BIKESHED_FENCE_H__ */