include/linux/scatterlist.h

   1 #ifndef _LINUX_SCATTERLIST_H
   2 #define _LINUX_SCATTERLIST_H
   3
   4 #include <asm/types.h>
   5 #include <asm/scatterlist.h>
   6 #include <linux/mm.h>
   7 #include <linux/string.h>
   8 #include <asm/io.h>
   9
  10 /*
  11  * Notes on SG table design.
  12  *
  13  * Architectures must provide an unsigned long page_link field in the
  14  * scatterlist struct. We use that to place the page pointer AND encode
  15  * information about the sg table as well. The two lower bits are reserved
  16  * for this information.
  17  *
  18  * If bit 0 is set, then the page_link contains a pointer to the next sg
  19  * table list. Otherwise the next entry is at sg + 1.
  20  *
  21  * If bit 1 is set, then this sg entry is the last element in a list.
  22  *
  23  * See sg_next().
  24  *
  25  */
  26
  27 #define SG_MAGIC        0x87654321
  28
  29 /**
  30  * sg_assign_page - Assign a given page to an SG entry
  31  * @sg:             SG entry
  32  * @page:           The page
  33  *
  34  * Description:
  35  *   Assign page to sg entry. Also see sg_set_page(), the most commonly used
  36  *   variant.
  37  *
  38  **/
  39 static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
  40 {
  41         unsigned long page_link = sg->page_link & 0x3;
  42
  43         /*
  44          * In order for the low bit stealing approach to work, pages
  45          * must be aligned at a 32-bit boundary as a minimum.
  46          */
  47         BUG_ON((unsigned long) page & 0x03);
  48 #ifdef CONFIG_DEBUG_SG
  49         BUG_ON(sg->sg_magic != SG_MAGIC);
  50 #endif
  51         sg->page_link = page_link | (unsigned long) page;
  52 }
  53
  54 /**
  55  * sg_set_page - Set sg entry to point at given page
  56  * @sg:          SG entry
  57  * @page:        The page
  58  * @len:         Length of data
  59  * @offset:      Offset into page
  60  *
  61  * Description:
  62  *   Use this function to set an sg entry pointing at a page, never assign
  63  *   the page directly. We encode sg table information in the lower bits
  64  *   of the page pointer. See sg_page() for looking up the page belonging
  65  *   to an sg entry.
  66  *
  67  **/
  68 static inline void sg_set_page(struct scatterlist *sg, struct page *page,
  69                                unsigned int len, unsigned int offset)
  70 {
  71         sg_assign_page(sg, page);
  72         sg->offset = offset;
  73         sg->length = len;
  74 }
  75
  76 #define sg_page(sg)     ((struct page *) ((sg)->page_link & ~0x3))
  77
  78 /**
  79  * sg_set_buf - Set sg entry to point at given data
  80  * @sg:          SG entry
  81  * @buf:         Data
  82  * @buflen:      Data length
  83  *
  84  **/
  85 static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
  86                               unsigned int buflen)
  87 {
  88         sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
  89 }
  90
  91 /*
  92  * We overload the LSB of the page pointer to indicate whether it's
  93  * a valid sg entry, or whether it points to the start of a new scatterlist.
  94  * Those low bits are there for everyone! (thanks mason :-)
  95  */
  96 #define sg_is_chain(sg)         ((sg)->page_link & 0x01)
  97 #define sg_is_last(sg)          ((sg)->page_link & 0x02)
  98 #define sg_chain_ptr(sg)        \
  99         ((struct scatterlist *) ((sg)->page_link & ~0x03))
 100
 101 /**
 102  * sg_next - return the next scatterlist entry in a list
 103  * @sg:         The current sg entry
 104  *
 105  * Description:
 106  *   Usually the next entry will be @sg@ + 1, but if this sg element is part
 107  *   of a chained scatterlist, it could jump to the start of a new
 108  *   scatterlist array.
 109  *
 110  **/
 111 static inline struct scatterlist *sg_next(struct scatterlist *sg)
 112 {
 113 #ifdef CONFIG_DEBUG_SG
 114         BUG_ON(sg->sg_magic != SG_MAGIC);
 115 #endif
 116         if (sg_is_last(sg))
 117                 return NULL;
 118
 119         sg++;
 120         if (unlikely(sg_is_chain(sg)))
 121                 sg = sg_chain_ptr(sg);
 122
 123         return sg;
 124 }
 125
 126 /*
 127  * Loop over each sg element, following the pointer to a new list if necessary
 128  */
 129 #define for_each_sg(sglist, sg, nr, __i)        \
 130         for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
 131
 132 /**
 133  * sg_last - return the last scatterlist entry in a list
 134  * @sgl:        First entry in the scatterlist
 135  * @nents:      Number of entries in the scatterlist
 136  *
 137  * Description:
 138  *   Should only be used casually, it (currently) scan the entire list
 139  *   to get the last entry.
 140  *
 141  *   Note that the @sgl@ pointer passed in need not be the first one,
 142  *   the important bit is that @nents@ denotes the number of entries that
 143  *   exist from @sgl@.
 144  *
 145  **/
 146 static inline struct scatterlist *sg_last(struct scatterlist *sgl,
 147                                           unsigned int nents)
 148 {
 149 #ifndef ARCH_HAS_SG_CHAIN
 150         struct scatterlist *ret = &sgl[nents - 1];
 151 #else
 152         struct scatterlist *sg, *ret = NULL;
 153         unsigned int i;
 154
 155         for_each_sg(sgl, sg, nents, i)
 156                 ret = sg;
 157
 158 #endif
 159 #ifdef CONFIG_DEBUG_SG
 160         BUG_ON(sgl[0].sg_magic != SG_MAGIC);
 161         BUG_ON(!sg_is_last(ret));
 162 #endif
 163         return ret;
 164 }
 165
 166 /**
 167  * sg_chain - Chain two sglists together
 168  * @prv:        First scatterlist
 169  * @prv_nents:  Number of entries in prv
 170  * @sgl:        Second scatterlist
 171  *
 172  * Description:
 173  *   Links @prv@ and @sgl@ together, to form a longer scatterlist.
 174  *
 175  **/
 176 static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
 177                             struct scatterlist *sgl)
 178 {
 179 #ifndef ARCH_HAS_SG_CHAIN
 180         BUG();
 181 #endif
 182         /*
 183          * Set lowest bit to indicate a link pointer, and make sure to clear
 184          * the termination bit if it happens to be set.
 185          */
 186         prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
 187 }
 188
 189 /**
 190  * sg_mark_end - Mark the end of the scatterlist
 191  * @sg:          SG entryScatterlist
 192  *
 193  * Description:
 194  *   Marks the passed in sg entry as the termination point for the sg
 195  *   table. A call to sg_next() on this entry will return NULL.
 196  *
 197  **/
 198 static inline void sg_mark_end(struct scatterlist *sg)
 199 {
 200 #ifdef CONFIG_DEBUG_SG
 201         BUG_ON(sg->sg_magic != SG_MAGIC);
 202 #endif
 203         /*
 204          * Set termination bit, clear potential chain bit
 205          */
 206         sg->page_link |= 0x02;
 207         sg->page_link &= ~0x01;
 208 }
 209
 210 /**
 211  * sg_init_table - Initialize SG table
 212  * @sgl:           The SG table
 213  * @nents:         Number of entries in table
 214  *
 215  * Notes:
 216  *   If this is part of a chained sg table, sg_mark_end() should be
 217  *   used only on the last table part.
 218  *
 219  **/
 220 static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
 221 {
 222         memset(sgl, 0, sizeof(*sgl) * nents);
 223 #ifdef CONFIG_DEBUG_SG
 224         {
 225                 unsigned int i;
 226                 for (i = 0; i < nents; i++)
 227                         sgl[i].sg_magic = SG_MAGIC;
 228         }
 229 #endif
 230         sg_mark_end(&sgl[nents - 1]);
 231 }
 232
 233 /**
 234  * sg_init_one - Initialize a single entry sg list
 235  * @sg:          SG entry
 236  * @buf:         Virtual address for IO
 237  * @buflen:      IO length
 238  *
 239  * Notes:
 240  *   This should not be used on a single entry that is part of a larger
 241  *   table. Use sg_init_table() for that.
 242  *
 243  **/
 244 static inline void sg_init_one(struct scatterlist *sg, const void *buf,
 245                                unsigned int buflen)
 246 {
 247         sg_init_table(sg, 1);
 248         sg_set_buf(sg, buf, buflen);
 249 }
 250
 251 /**
 252  * sg_phys - Return physical address of an sg entry
 253  * @sg:      SG entry
 254  *
 255  * Description:
 256  *   This calls page_to_phys() on the page in this sg entry, and adds the
 257  *   sg offset. The caller must know that it is legal to call page_to_phys()
 258  *   on the sg page.
 259  *
 260  **/
 261 static inline dma_addr_t sg_phys(struct scatterlist *sg)
 262 {
 263         return page_to_phys(sg_page(sg)) + sg->offset;
 264 }
 265
 266 /**
 267  * sg_virt - Return virtual address of an sg entry
 268  * @sg:      SG entry
 269  *
 270  * Description:
 271  *   This calls page_address() on the page in this sg entry, and adds the
 272  *   sg offset. The caller must know that the sg page has a valid virtual
 273  *   mapping.
 274  *
 275  **/
 276 static inline void *sg_virt(struct scatterlist *sg)
 277 {
 278         return page_address(sg_page(sg)) + sg->offset;
 279 }
 280
 281 #endif /* _LINUX_SCATTERLIST_H */