include/linux/scatterlist.h

   1 #ifndef _LINUX_SCATTERLIST_H
   2 #define _LINUX_SCATTERLIST_H
   3
   4 #include <linux/string.h>
   5 #include <linux/bug.h>
   6 #include <linux/mm.h>
   7
   8 #include <asm/types.h>
   9 #include <asm/scatterlist.h>
  10 #include <asm/io.h>
  11
  12 struct sg_table {
  13         struct scatterlist *sgl;        /* the list */
  14         unsigned int nents;             /* number of mapped entries */
  15         unsigned int orig_nents;        /* original size of list */
  16 };
  17
  18 /*
  19  * Notes on SG table design.
  20  *
  21  * Architectures must provide an unsigned long page_link field in the
  22  * scatterlist struct. We use that to place the page pointer AND encode
  23  * information about the sg table as well. The two lower bits are reserved
  24  * for this information.
  25  *
  26  * If bit 0 is set, then the page_link contains a pointer to the next sg
  27  * table list. Otherwise the next entry is at sg + 1.
  28  *
  29  * If bit 1 is set, then this sg entry is the last element in a list.
  30  *
  31  * See sg_next().
  32  *
  33  */
  34
  35 #define SG_MAGIC        0x87654321
  36
  37 /*
  38  * We overload the LSB of the page pointer to indicate whether it's
  39  * a valid sg entry, or whether it points to the start of a new scatterlist.
  40  * Those low bits are there for everyone! (thanks mason :-)
  41  */
  42 #define sg_is_chain(sg)         ((sg)->page_link & 0x01)
  43 #define sg_is_last(sg)          ((sg)->page_link & 0x02)
  44 #define sg_chain_ptr(sg)        \
  45         ((struct scatterlist *) ((sg)->page_link & ~0x03))
  46
  47 /**
  48  * sg_assign_page - Assign a given page to an SG entry
  49  * @sg:             SG entry
  50  * @page:           The page
  51  *
  52  * Description:
  53  *   Assign page to sg entry. Also see sg_set_page(), the most commonly used
  54  *   variant.
  55  *
  56  **/
  57 static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
  58 {
  59         unsigned long page_link = sg->page_link & 0x3;
  60
  61         /*
  62          * In order for the low bit stealing approach to work, pages
  63          * must be aligned at a 32-bit boundary as a minimum.
  64          */
  65         BUG_ON((unsigned long) page & 0x03);
  66 #ifdef CONFIG_DEBUG_SG
  67         BUG_ON(sg->sg_magic != SG_MAGIC);
  68         BUG_ON(sg_is_chain(sg));
  69 #endif
  70         sg->page_link = page_link | (unsigned long) page;
  71 }
  72
  73 /**
  74  * sg_set_page - Set sg entry to point at given page
  75  * @sg:          SG entry
  76  * @page:        The page
  77  * @len:         Length of data
  78  * @offset:      Offset into page
  79  *
  80  * Description:
  81  *   Use this function to set an sg entry pointing at a page, never assign
  82  *   the page directly. We encode sg table information in the lower bits
  83  *   of the page pointer. See sg_page() for looking up the page belonging
  84  *   to an sg entry.
  85  *
  86  **/
  87 static inline void sg_set_page(struct scatterlist *sg, struct page *page,
  88                                unsigned int len, unsigned int offset)
  89 {
  90         sg_assign_page(sg, page);
  91         sg->offset = offset;
  92         sg->length = len;
  93 }
  94
  95 static inline struct page *sg_page(struct scatterlist *sg)
  96 {
  97 #ifdef CONFIG_DEBUG_SG
  98         BUG_ON(sg->sg_magic != SG_MAGIC);
  99         BUG_ON(sg_is_chain(sg));
 100 #endif
 101         return (struct page *)((sg)->page_link & ~0x3);
 102 }
 103
 104 /**
 105  * sg_set_buf - Set sg entry to point at given data
 106  * @sg:          SG entry
 107  * @buf:         Data
 108  * @buflen:      Data length
 109  *
 110  **/
 111 static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
 112                               unsigned int buflen)
 113 {
 114         sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
 115 }
 116
 117 /*
 118  * Loop over each sg element, following the pointer to a new list if necessary
 119  */
 120 #define for_each_sg(sglist, sg, nr, __i)        \
 121         for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
 122
 123 /**
 124  * sg_chain - Chain two sglists together
 125  * @prv:        First scatterlist
 126  * @prv_nents:  Number of entries in prv
 127  * @sgl:        Second scatterlist
 128  *
 129  * Description:
 130  *   Links @prv@ and @sgl@ together, to form a longer scatterlist.
 131  *
 132  **/
 133 static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
 134                             struct scatterlist *sgl)
 135 {
 136 #ifndef ARCH_HAS_SG_CHAIN
 137         BUG();
 138 #endif
 139
 140         /*
 141          * offset and length are unused for chain entry.  Clear them.
 142          */
 143         prv[prv_nents - 1].offset = 0;
 144         prv[prv_nents - 1].length = 0;
 145
 146         /*
 147          * Set lowest bit to indicate a link pointer, and make sure to clear
 148          * the termination bit if it happens to be set.
 149          */
 150         prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
 151 }
 152
 153 /**
 154  * sg_mark_end - Mark the end of the scatterlist
 155  * @sg:          SG entryScatterlist
 156  *
 157  * Description:
 158  *   Marks the passed in sg entry as the termination point for the sg
 159  *   table. A call to sg_next() on this entry will return NULL.
 160  *
 161  **/
 162 static inline void sg_mark_end(struct scatterlist *sg)
 163 {
 164 #ifdef CONFIG_DEBUG_SG
 165         BUG_ON(sg->sg_magic != SG_MAGIC);
 166 #endif
 167         /*
 168          * Set termination bit, clear potential chain bit
 169          */
 170         sg->page_link |= 0x02;
 171         sg->page_link &= ~0x01;
 172 }
 173
 174 /**
 175  * sg_phys - Return physical address of an sg entry
 176  * @sg:      SG entry
 177  *
 178  * Description:
 179  *   This calls page_to_phys() on the page in this sg entry, and adds the
 180  *   sg offset. The caller must know that it is legal to call page_to_phys()
 181  *   on the sg page.
 182  *
 183  **/
 184 static inline dma_addr_t sg_phys(struct scatterlist *sg)
 185 {
 186         return page_to_phys(sg_page(sg)) + sg->offset;
 187 }
 188
 189 /**
 190  * sg_virt - Return virtual address of an sg entry
 191  * @sg:      SG entry
 192  *
 193  * Description:
 194  *   This calls page_address() on the page in this sg entry, and adds the
 195  *   sg offset. The caller must know that the sg page has a valid virtual
 196  *   mapping.
 197  *
 198  **/
 199 static inline void *sg_virt(struct scatterlist *sg)
 200 {
 201         return page_address(sg_page(sg)) + sg->offset;
 202 }
 203
 204 struct scatterlist *sg_next(struct scatterlist *);
 205 struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
 206 void sg_init_table(struct scatterlist *, unsigned int);
 207 void sg_init_one(struct scatterlist *, const void *, unsigned int);
 208
 209 typedef struct scatterlist *(sg_alloc_fn)(unsigned int, gfp_t);
 210 typedef void (sg_free_fn)(struct scatterlist *, unsigned int);
 211
 212 void __sg_free_table(struct sg_table *, unsigned int, sg_free_fn *);
 213 void sg_free_table(struct sg_table *);
 214 int __sg_alloc_table(struct sg_table *, unsigned int, unsigned int, gfp_t,
 215                      sg_alloc_fn *);
 216 int sg_alloc_table(struct sg_table *, unsigned int, gfp_t);
 217
 218 size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
 219                            void *buf, size_t buflen);
 220 size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
 221                          void *buf, size_t buflen);
 222
 223 /*
 224  * Maximum number of entries that will be allocated in one piece, if
 225  * a list larger than this is required then chaining will be utilized.
 226  */
 227 #define SG_MAX_SINGLE_ALLOC             (PAGE_SIZE / sizeof(struct scatterlist))
 228
 229
 230 /*
 231  * Mapping sg iterator
 232  *
 233  * Iterates over sg entries mapping page-by-page.  On each successful
 234  * iteration, @miter->page points to the mapped page and
 235  * @miter->length bytes of data can be accessed at @miter->addr.  As
 236  * long as an interation is enclosed between start and stop, the user
 237  * is free to choose control structure and when to stop.
 238  *
 239  * @miter->consumed is set to @miter->length on each iteration.  It
 240  * can be adjusted if the user can't consume all the bytes in one go.
 241  * Also, a stopped iteration can be resumed by calling next on it.
 242  * This is useful when iteration needs to release all resources and
 243  * continue later (e.g. at the next interrupt).
 244  */
 245
 246 #define SG_MITER_ATOMIC         (1 << 0)         /* use kmap_atomic */
 247 #define SG_MITER_TO_SG          (1 << 1)        /* flush back to phys on unmap */
 248 #define SG_MITER_FROM_SG        (1 << 2)        /* nop */
 249
 250 struct sg_mapping_iter {
 251         /* the following three fields can be accessed directly */
 252         struct page             *page;          /* currently mapped page */
 253         void                    *addr;          /* pointer to the mapped area */
 254         size_t                  length;         /* length of the mapped area */
 255         size_t                  consumed;       /* number of consumed bytes */
 256
 257         /* these are internal states, keep away */
 258         struct scatterlist      *__sg;          /* current entry */
 259         unsigned int            __nents;        /* nr of remaining entries */
 260         unsigned int            __offset;       /* offset within sg */
 261         unsigned int            __flags;
 262 };
 263
 264 void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
 265                     unsigned int nents, unsigned int flags);
 266 bool sg_miter_next(struct sg_mapping_iter *miter);
 267 void sg_miter_stop(struct sg_mapping_iter *miter);
 268
 269 #endif /* _LINUX_SCATTERLIST_H */