include/linux/dma-buf-map.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  * Pointer to dma-buf-mapped memory, plus helpers.
   4  */
   5
   6 #ifndef __DMA_BUF_MAP_H__
   7 #define __DMA_BUF_MAP_H__
   8
   9 #include <linux/io.h>
  10 #include <linux/string.h>
  11
  12 /**
  13  * DOC: overview
  14  *
  15  * Calling dma-buf's vmap operation returns a pointer to the buffer's memory.
  16  * Depending on the location of the buffer, users may have to access it with
  17  * I/O operations or memory load/store operations. For example, copying to
  18  * system memory could be done with memcpy(), copying to I/O memory would be
  19  * done with memcpy_toio().
  20  *
  21  * .. code-block:: c
  22  *
  23  *      void *vaddr = ...; // pointer to system memory
  24  *      memcpy(vaddr, src, len);
  25  *
  26  *      void *vaddr_iomem = ...; // pointer to I/O memory
  27  *      memcpy_toio(vaddr, _iomem, src, len);
  28  *
  29  * When using dma-buf's vmap operation, the returned pointer is encoded as
  30  * :c:type:`struct dma_buf_map <dma_buf_map>`.
  31  * :c:type:`struct dma_buf_map <dma_buf_map>` stores the buffer's address in
  32  * system or I/O memory and a flag that signals the required method of
  33  * accessing the buffer. Use the returned instance and the helper functions
  34  * to access the buffer's memory in the correct way.
  35  *
  36  * The type :c:type:`struct dma_buf_map <dma_buf_map>` and its helpers are
  37  * actually independent from the dma-buf infrastructure. When sharing buffers
  38  * among devices, drivers have to know the location of the memory to access
  39  * the buffers in a safe way. :c:type:`struct dma_buf_map <dma_buf_map>`
  40  * solves this problem for dma-buf and its users. If other drivers or
  41  * sub-systems require similar functionality, the type could be generalized
  42  * and moved to a more prominent header file.
  43  *
  44  * Open-coding access to :c:type:`struct dma_buf_map <dma_buf_map>` is
  45  * considered bad style. Rather then accessing its fields directly, use one
  46  * of the provided helper functions, or implement your own. For example,
  47  * instances of :c:type:`struct dma_buf_map <dma_buf_map>` can be initialized
  48  * statically with DMA_BUF_MAP_INIT_VADDR(), or at runtime with
  49  * dma_buf_map_set_vaddr(). These helpers will set an address in system memory.
  50  *
  51  * .. code-block:: c
  52  *
  53  *      struct dma_buf_map map = DMA_BUF_MAP_INIT_VADDR(0xdeadbeaf);
  54  *
  55  *      dma_buf_map_set_vaddr(&map. 0xdeadbeaf);
  56  *
  57  * To set an address in I/O memory, use dma_buf_map_set_vaddr_iomem().
  58  *
  59  * .. code-block:: c
  60  *
  61  *      dma_buf_map_set_vaddr_iomem(&map. 0xdeadbeaf);
  62  *
  63  * Instances of struct dma_buf_map do not have to be cleaned up, but
  64  * can be cleared to NULL with dma_buf_map_clear(). Cleared mappings
  65  * always refer to system memory.
  66  *
  67  * .. code-block:: c
  68  *
  69  *      dma_buf_map_clear(&map);
  70  *
  71  * Test if a mapping is valid with either dma_buf_map_is_set() or
  72  * dma_buf_map_is_null().
  73  *
  74  * .. code-block:: c
  75  *
  76  *      if (dma_buf_map_is_set(&map) != dma_buf_map_is_null(&map))
  77  *              // always true
  78  *
  79  * Instances of :c:type:`struct dma_buf_map <dma_buf_map>` can be compared
  80  * for equality with dma_buf_map_is_equal(). Mappings the point to different
  81  * memory spaces, system or I/O, are never equal. That's even true if both
  82  * spaces are located in the same address space, both mappings contain the
  83  * same address value, or both mappings refer to NULL.
  84  *
  85  * .. code-block:: c
  86  *
  87  *      struct dma_buf_map sys_map; // refers to system memory
  88  *      struct dma_buf_map io_map; // refers to I/O memory
  89  *
  90  *      if (dma_buf_map_is_equal(&sys_map, &io_map))
  91  *              // always false
  92  *
  93  * A set up instance of struct dma_buf_map can be used to access or manipulate
  94  * the buffer memory. Depending on the location of the memory, the provided
  95  * helpers will pick the correct operations. Data can be copied into the memory
  96  * with dma_buf_map_memcpy_to(). The address can be manipulated with
  97  * dma_buf_map_incr().
  98  *
  99  * .. code-block:: c
 100  *
 101  *      const void *src = ...; // source buffer
 102  *      size_t len = ...; // length of src
 103  *
 104  *      dma_buf_map_memcpy_to(&map, src, len);
 105  *      dma_buf_map_incr(&map, len); // go to first byte after the memcpy
 106  */
 107
 108 /**
 109  * struct dma_buf_map - Pointer to vmap'ed dma-buf memory.
 110  * @vaddr_iomem:        The buffer's address if in I/O memory
 111  * @vaddr:              The buffer's address if in system memory
 112  * @is_iomem:           True if the dma-buf memory is located in I/O
 113  *                      memory, or false otherwise.
 114  */
 115 struct dma_buf_map {
 116         union {
 117                 void __iomem *vaddr_iomem;
 118                 void *vaddr;
 119         };
 120         bool is_iomem;
 121 };
 122
 123 /**
 124  * DMA_BUF_MAP_INIT_VADDR - Initializes struct dma_buf_map to an address in system memory
 125  * @vaddr_:     A system-memory address
 126  */
 127 #define DMA_BUF_MAP_INIT_VADDR(vaddr_) \
 128         { \
 129                 .vaddr = (vaddr_), \
 130                 .is_iomem = false, \
 131         }
 132
 133 /**
 134  * dma_buf_map_set_vaddr - Sets a dma-buf mapping structure to an address in system memory
 135  * @map:        The dma-buf mapping structure
 136  * @vaddr:      A system-memory address
 137  *
 138  * Sets the address and clears the I/O-memory flag.
 139  */
 140 static inline void dma_buf_map_set_vaddr(struct dma_buf_map *map, void *vaddr)
 141 {
 142         map->vaddr = vaddr;
 143         map->is_iomem = false;
 144 }
 145
 146 /**
 147  * dma_buf_map_set_vaddr_iomem - Sets a dma-buf mapping structure to an address in I/O memory
 148  * @map:                The dma-buf mapping structure
 149  * @vaddr_iomem:        An I/O-memory address
 150  *
 151  * Sets the address and the I/O-memory flag.
 152  */
 153 static inline void dma_buf_map_set_vaddr_iomem(struct dma_buf_map *map,
 154                                                void __iomem *vaddr_iomem)
 155 {
 156         map->vaddr_iomem = vaddr_iomem;
 157         map->is_iomem = true;
 158 }
 159
 160 /**
 161  * dma_buf_map_is_equal - Compares two dma-buf mapping structures for equality
 162  * @lhs:        The dma-buf mapping structure
 163  * @rhs:        A dma-buf mapping structure to compare with
 164  *
 165  * Two dma-buf mapping structures are equal if they both refer to the same type of memory
 166  * and to the same address within that memory.
 167  *
 168  * Returns:
 169  * True is both structures are equal, or false otherwise.
 170  */
 171 static inline bool dma_buf_map_is_equal(const struct dma_buf_map *lhs,
 172                                         const struct dma_buf_map *rhs)
 173 {
 174         if (lhs->is_iomem != rhs->is_iomem)
 175                 return false;
 176         else if (lhs->is_iomem)
 177                 return lhs->vaddr_iomem == rhs->vaddr_iomem;
 178         else
 179                 return lhs->vaddr == rhs->vaddr;
 180 }
 181
 182 /**
 183  * dma_buf_map_is_null - Tests for a dma-buf mapping to be NULL
 184  * @map:        The dma-buf mapping structure
 185  *
 186  * Depending on the state of struct dma_buf_map.is_iomem, tests if the
 187  * mapping is NULL.
 188  *
 189  * Returns:
 190  * True if the mapping is NULL, or false otherwise.
 191  */
 192 static inline bool dma_buf_map_is_null(const struct dma_buf_map *map)
 193 {
 194         if (map->is_iomem)
 195                 return !map->vaddr_iomem;
 196         return !map->vaddr;
 197 }
 198
 199 /**
 200  * dma_buf_map_is_set - Tests is the dma-buf mapping has been set
 201  * @map:        The dma-buf mapping structure
 202  *
 203  * Depending on the state of struct dma_buf_map.is_iomem, tests if the
 204  * mapping has been set.
 205  *
 206  * Returns:
 207  * True if the mapping is been set, or false otherwise.
 208  */
 209 static inline bool dma_buf_map_is_set(const struct dma_buf_map *map)
 210 {
 211         return !dma_buf_map_is_null(map);
 212 }
 213
 214 /**
 215  * dma_buf_map_clear - Clears a dma-buf mapping structure
 216  * @map:        The dma-buf mapping structure
 217  *
 218  * Clears all fields to zero; including struct dma_buf_map.is_iomem. So
 219  * mapping structures that were set to point to I/O memory are reset for
 220  * system memory. Pointers are cleared to NULL. This is the default.
 221  */
 222 static inline void dma_buf_map_clear(struct dma_buf_map *map)
 223 {
 224         if (map->is_iomem) {
 225                 map->vaddr_iomem = NULL;
 226                 map->is_iomem = false;
 227         } else {
 228                 map->vaddr = NULL;
 229         }
 230 }
 231
 232 /**
 233  * dma_buf_map_memcpy_to - Memcpy into dma-buf mapping
 234  * @dst:        The dma-buf mapping structure
 235  * @src:        The source buffer
 236  * @len:        The number of byte in src
 237  *
 238  * Copies data into a dma-buf mapping. The source buffer is in system
 239  * memory. Depending on the buffer's location, the helper picks the correct
 240  * method of accessing the memory.
 241  */
 242 static inline void dma_buf_map_memcpy_to(struct dma_buf_map *dst, const void *src, size_t len)
 243 {
 244         if (dst->is_iomem)
 245                 memcpy_toio(dst->vaddr_iomem, src, len);
 246         else
 247                 memcpy(dst->vaddr, src, len);
 248 }
 249
 250 /**
 251  * dma_buf_map_incr - Increments the address stored in a dma-buf mapping
 252  * @map:        The dma-buf mapping structure
 253  * @incr:       The number of bytes to increment
 254  *
 255  * Increments the address stored in a dma-buf mapping. Depending on the
 256  * buffer's location, the correct value will be updated.
 257  */
 258 static inline void dma_buf_map_incr(struct dma_buf_map *map, size_t incr)
 259 {
 260         if (map->is_iomem)
 261                 map->vaddr_iomem += incr;
 262         else
 263                 map->vaddr += incr;
 264 }
 265
 266 #endif /* __DMA_BUF_MAP_H__ */