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Filename : dma-buf-map.h
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/* 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>
#include <linux/string.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.
 *
 * 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.
 *
 * 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);
 *
 * To set an address in I/O memory, use dma_buf_map_set_vaddr_iomem().
 *
 * .. code-block:: c
 *
 *	dma_buf_map_set_vaddr_iomem(&map. 0xdeadbeaf);
 *
 * 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.
 *
 * .. code-block:: c
 *
 *	dma_buf_map_clear(&map);
 *
 * 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
 *
 * A set up instance of struct dma_buf_map can be used to access or manipulate
 * the buffer memory. Depending on the location of the memory, the provided
 * helpers will pick the correct operations. Data can be copied into the memory
 * with dma_buf_map_memcpy_to(). The address can be manipulated with
 * dma_buf_map_incr().
 *
 * .. code-block:: c
 *
 *	const void *src = ...; // source buffer
 *	size_t len = ...; // length of src
 *
 *	dma_buf_map_memcpy_to(&map, src, len);
 *	dma_buf_map_incr(&map, len); // go to first byte after the memcpy
 */

/**
 * 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_set_vaddr_iomem - Sets a dma-buf mapping structure to an address in I/O memory
 * @map:		The dma-buf mapping structure
 * @vaddr_iomem:	An I/O-memory address
 *
 * Sets the address and the I/O-memory flag.
 */
static inline void dma_buf_map_set_vaddr_iomem(struct dma_buf_map *map,
					       void __iomem *vaddr_iomem)
{
	map->vaddr_iomem = vaddr_iomem;
	map->is_iomem = true;
}

/**
 * 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;
	}
}

/**
 * dma_buf_map_memcpy_to - Memcpy into dma-buf mapping
 * @dst:	The dma-buf mapping structure
 * @src:	The source buffer
 * @len:	The number of byte in src
 *
 * Copies data into a dma-buf mapping. The source buffer is in system
 * memory. Depending on the buffer's location, the helper picks the correct
 * method of accessing the memory.
 */
static inline void dma_buf_map_memcpy_to(struct dma_buf_map *dst, const void *src, size_t len)
{
	if (dst->is_iomem)
		memcpy_toio(dst->vaddr_iomem, src, len);
	else
		memcpy(dst->vaddr, src, len);
}

/**
 * dma_buf_map_incr - Increments the address stored in a dma-buf mapping
 * @map:	The dma-buf mapping structure
 * @incr:	The number of bytes to increment
 *
 * Increments the address stored in a dma-buf mapping. Depending on the
 * buffer's location, the correct value will be updated.
 */
static inline void dma_buf_map_incr(struct dma_buf_map *map, size_t incr)
{
	if (map->is_iomem)
		map->vaddr_iomem += incr;
	else
		map->vaddr += incr;
}

#endif /* __DMA_BUF_MAP_H__ */