1 files changed, 193 insertions, 0 deletions
diff --git a/include/linux/dma-buf-map.h b/include/linux/dma-buf-map.h
new file mode 100644
index 000000000000..fd1aba545fdf
--- /dev/null
+++ b/include/linux/dma-buf-map.h
@@ -0,0 +1,193 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Pointer to dma-buf-mapped memory, plus helpers.
+ */
+
+#ifndef __DMA_BUF_MAP_H__
+#define __DMA_BUF_MAP_H__
+
+#include <linux/io.h>
+
+/**
+ * DOC: overview
+ *
+ * Calling dma-buf's vmap operation returns a pointer to the buffer's memory.
+ * Depending on the location of the buffer, users may have to access it with
+ * I/O operations or memory load/store operations. For example, copying to
+ * system memory could be done with memcpy(), copying to I/O memory would be
+ * done with memcpy_toio().
+ *
+ * .. code-block:: c
+ *
+ *	void *vaddr = ...; // pointer to system memory
+ *	memcpy(vaddr, src, len);
+ *
+ *	void *vaddr_iomem = ...; // pointer to I/O memory
+ *	memcpy_toio(vaddr, _iomem, src, len);
+ *
+ * When using dma-buf's vmap operation, the returned pointer is encoded as
+ * :c:type:`struct dma_buf_map <dma_buf_map>`.
+ * :c:type:`struct dma_buf_map <dma_buf_map>` stores the buffer's address in
+ * system or I/O memory and a flag that signals the required method of
+ * accessing the buffer. Use the returned instance and the helper functions
+ * to access the buffer's memory in the correct way.
+ *
+ * Open-coding access to :c:type:`struct dma_buf_map <dma_buf_map>` is
+ * considered bad style. Rather then accessing its fields directly, use one
+ * of the provided helper functions, or implement your own. For example,
+ * instances of :c:type:`struct dma_buf_map <dma_buf_map>` can be initialized
+ * statically with DMA_BUF_MAP_INIT_VADDR(), or at runtime with
+ * dma_buf_map_set_vaddr(). These helpers will set an address in system memory.
+ *
+ * .. code-block:: c
+ *
+ *	struct dma_buf_map map = DMA_BUF_MAP_INIT_VADDR(0xdeadbeaf);
+ *
+ *	dma_buf_map_set_vaddr(&map. 0xdeadbeaf);
+ *
+ * Test if a mapping is valid with either dma_buf_map_is_set() or
+ * dma_buf_map_is_null().
+ *
+ * .. code-block:: c
+ *
+ *	if (dma_buf_map_is_set(&map) != dma_buf_map_is_null(&map))
+ *		// always true
+ *
+ * Instances of :c:type:`struct dma_buf_map <dma_buf_map>` can be compared
+ * for equality with dma_buf_map_is_equal(). Mappings the point to different
+ * memory spaces, system or I/O, are never equal. That's even true if both
+ * spaces are located in the same address space, both mappings contain the
+ * same address value, or both mappings refer to NULL.
+ *
+ * .. code-block:: c
+ *
+ *	struct dma_buf_map sys_map; // refers to system memory
+ *	struct dma_buf_map io_map; // refers to I/O memory
+ *
+ *	if (dma_buf_map_is_equal(&sys_map, &io_map))
+ *		// always false
+ *
+ * Instances of struct dma_buf_map do not have to be cleaned up, but
+ * can be cleared to NULL with dma_buf_map_clear(). Cleared mappings
+ * always refer to system memory.
+ *
+ * The type :c:type:`struct dma_buf_map <dma_buf_map>` and its helpers are
+ * actually independent from the dma-buf infrastructure. When sharing buffers
+ * among devices, drivers have to know the location of the memory to access
+ * the buffers in a safe way. :c:type:`struct dma_buf_map <dma_buf_map>`
+ * solves this problem for dma-buf and its users. If other drivers or
+ * sub-systems require similar functionality, the type could be generalized
+ * and moved to a more prominent header file.
+ */
+
+/**
+ * struct dma_buf_map - Pointer to vmap'ed dma-buf memory.
+ * @vaddr_iomem:	The buffer's address if in I/O memory
+ * @vaddr:		The buffer's address if in system memory
+ * @is_iomem:		True if the dma-buf memory is located in I/O
+ *			memory, or false otherwise.
+ */
+struct dma_buf_map {
+	union {
+		void __iomem *vaddr_iomem;
+		void *vaddr;
+	};
+	bool is_iomem;
+};
+
+/**
+ * DMA_BUF_MAP_INIT_VADDR - Initializes struct dma_buf_map to an address in system memory
+ * @vaddr:	A system-memory address
+ */
+#define DMA_BUF_MAP_INIT_VADDR(vaddr_) \
+	{ \
+		.vaddr = (vaddr_), \
+		.is_iomem = false, \
+	}
+
+/**
+ * dma_buf_map_set_vaddr - Sets a dma-buf mapping structure to an address in system memory
+ * @map:	The dma-buf mapping structure
+ * @vaddr:	A system-memory address
+ *
+ * Sets the address and clears the I/O-memory flag.
+ */
+static inline void dma_buf_map_set_vaddr(struct dma_buf_map *map, void *vaddr)
+{
+	map->vaddr = vaddr;
+	map->is_iomem = false;
+}
+
+/**
+ * dma_buf_map_is_equal - Compares two dma-buf mapping structures for equality
+ * @lhs:	The dma-buf mapping structure
+ * @rhs:	A dma-buf mapping structure to compare with
+ *
+ * Two dma-buf mapping structures are equal if they both refer to the same type of memory
+ * and to the same address within that memory.
+ *
+ * Returns:
+ * True is both structures are equal, or false otherwise.
+ */
+static inline bool dma_buf_map_is_equal(const struct dma_buf_map *lhs,
+					const struct dma_buf_map *rhs)
+{
+	if (lhs->is_iomem != rhs->is_iomem)
+		return false;
+	else if (lhs->is_iomem)
+		return lhs->vaddr_iomem == rhs->vaddr_iomem;
+	else
+		return lhs->vaddr == rhs->vaddr;
+}
+
+/**
+ * dma_buf_map_is_null - Tests for a dma-buf mapping to be NULL
+ * @map:	The dma-buf mapping structure
+ *
+ * Depending on the state of struct dma_buf_map.is_iomem, tests if the
+ * mapping is NULL.
+ *
+ * Returns:
+ * True if the mapping is NULL, or false otherwise.
+ */
+static inline bool dma_buf_map_is_null(const struct dma_buf_map *map)
+{
+	if (map->is_iomem)
+		return !map->vaddr_iomem;
+	return !map->vaddr;
+}
+
+/**
+ * dma_buf_map_is_set - Tests is the dma-buf mapping has been set
+ * @map:	The dma-buf mapping structure
+ *
+ * Depending on the state of struct dma_buf_map.is_iomem, tests if the
+ * mapping has been set.
+ *
+ * Returns:
+ * True if the mapping is been set, or false otherwise.
+ */
+static inline bool dma_buf_map_is_set(const struct dma_buf_map *map)
+{
+	return !dma_buf_map_is_null(map);
+}
+
+/**
+ * dma_buf_map_clear - Clears a dma-buf mapping structure
+ * @map:	The dma-buf mapping structure
+ *
+ * Clears all fields to zero; including struct dma_buf_map.is_iomem. So
+ * mapping structures that were set to point to I/O memory are reset for
+ * system memory. Pointers are cleared to NULL. This is the default.
+ */
+static inline void dma_buf_map_clear(struct dma_buf_map *map)
+{
+	if (map->is_iomem) {
+		map->vaddr_iomem = NULL;
+		map->is_iomem = false;
+	} else {
+		map->vaddr = NULL;
+	}
+}
+
+#endif /* __DMA_BUF_MAP_H__ */