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  * We overload the LSB of the page pointer to indicate whether it's
  31  * a valid sg entry, or whether it points to the start of a new scatterlist.
  32  * Those low bits are there for everyone! (thanks mason :-)
  33  */
  34 #define sg_is_chain(sg)         ((sg)->page_link & 0x01)
  35 #define sg_is_last(sg)          ((sg)->page_link & 0x02)
  36 #define sg_chain_ptr(sg)        \
  37         ((struct scatterlist *) ((sg)->page_link & ~0x03))
  38
  39 /**
  40  * sg_assign_page - Assign a given page to an SG entry
  41  * @sg:             SG entry
  42  * @page:           The page
  43  *
  44  * Description:
  45  *   Assign page to sg entry. Also see sg_set_page(), the most commonly used
  46  *   variant.
  47  *
  48  **/
  49 static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
  50 {
  51         unsigned long page_link = sg->page_link & 0x3;
  52
  53         /*
  54          * In order for the low bit stealing approach to work, pages
  55          * must be aligned at a 32-bit boundary as a minimum.
  56          */
  57         BUG_ON((unsigned long) page & 0x03);
  58 #ifdef CONFIG_DEBUG_SG
  59         BUG_ON(sg->sg_magic != SG_MAGIC);
  60         BUG_ON(sg_is_chain(sg));
  61 #endif
  62         sg->page_link = page_link | (unsigned long) page;
  63 }
  64
  65 /**
  66  * sg_set_page - Set sg entry to point at given page
  67  * @sg:          SG entry
  68  * @page:        The page
  69  * @len:         Length of data
  70  * @offset:      Offset into page
  71  *
  72  * Description:
  73  *   Use this function to set an sg entry pointing at a page, never assign
  74  *   the page directly. We encode sg table information in the lower bits
  75  *   of the page pointer. See sg_page() for looking up the page belonging
  76  *   to an sg entry.
  77  *
  78  **/
  79 static inline void sg_set_page(struct scatterlist *sg, struct page *page,
  80                                unsigned int len, unsigned int offset)
  81 {
  82         sg_assign_page(sg, page);
  83         sg->offset = offset;
  84         sg->length = len;
  85 }
  86
  87 static inline struct page *sg_page(struct scatterlist *sg)
  88 {
  89 #ifdef CONFIG_DEBUG_SG
  90         BUG_ON(sg->sg_magic != SG_MAGIC);
  91         BUG_ON(sg_is_chain(sg));
  92 #endif
  93         return (struct page *)((sg)->page_link & ~0x3);
  94 }
  95
  96 /**
  97  * sg_set_buf - Set sg entry to point at given data
  98  * @sg:          SG entry
  99  * @buf:         Data
 100  * @buflen:      Data length
 101  *
 102  **/
 103 static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
 104                               unsigned int buflen)
 105 {
 106         sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
 107 }
 108
 109 /**
 110  * sg_next - return the next scatterlist entry in a list
 111  * @sg:         The current sg entry
 112  *
 113  * Description:
 114  *   Usually the next entry will be @sg@ + 1, but if this sg element is part
 115  *   of a chained scatterlist, it could jump to the start of a new
 116  *   scatterlist array.
 117  *
 118  **/
 119 static inline struct scatterlist *sg_next(struct scatterlist *sg)
 120 {
 121 #ifdef CONFIG_DEBUG_SG
 122         BUG_ON(sg->sg_magic != SG_MAGIC);
 123 #endif
 124         if (sg_is_last(sg))
 125                 return NULL;
 126
 127         sg++;
 128         if (unlikely(sg_is_chain(sg)))
 129                 sg = sg_chain_ptr(sg);
 130
 131         return sg;
 132 }
 133
 134 /*
 135  * Loop over each sg element, following the pointer to a new list if necessary
 136  */
 137 #define for_each_sg(sglist, sg, nr, __i)        \
 138         for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
 139
 140 /**
 141  * sg_last - return the last scatterlist entry in a list
 142  * @sgl:        First entry in the scatterlist
 143  * @nents:      Number of entries in the scatterlist
 144  *
 145  * Description:
 146  *   Should only be used casually, it (currently) scan the entire list
 147  *   to get the last entry.
 148  *
 149  *   Note that the @sgl@ pointer passed in need not be the first one,
 150  *   the important bit is that @nents@ denotes the number of entries that
 151  *   exist from @sgl@.
 152  *
 153  **/
 154 static inline struct scatterlist *sg_last(struct scatterlist *sgl,
 155                                           unsigned int nents)
 156 {
 157 #ifndef ARCH_HAS_SG_CHAIN
 158         struct scatterlist *ret = &sgl[nents - 1];
 159 #else
 160         struct scatterlist *sg, *ret = NULL;
 161         unsigned int i;
 162
 163         for_each_sg(sgl, sg, nents, i)
 164                 ret = sg;
 165
 166 #endif
 167 #ifdef CONFIG_DEBUG_SG
 168         BUG_ON(sgl[0].sg_magic != SG_MAGIC);
 169         BUG_ON(!sg_is_last(ret));
 170 #endif
 171         return ret;
 172 }
 173
 174 /**
 175  * sg_chain - Chain two sglists together
 176  * @prv:        First scatterlist
 177  * @prv_nents:  Number of entries in prv
 178  * @sgl:        Second scatterlist
 179  *
 180  * Description:
 181  *   Links @prv@ and @sgl@ together, to form a longer scatterlist.
 182  *
 183  **/
 184 static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
 185                             struct scatterlist *sgl)
 186 {
 187 #ifndef ARCH_HAS_SG_CHAIN
 188         BUG();
 189 #endif
 190
 191         /*
 192          * offset and length are unused for chain entry.  Clear them.
 193          */
 194         prv->offset = 0;
 195         prv->length = 0;
 196
 197         /*
 198          * Set lowest bit to indicate a link pointer, and make sure to clear
 199          * the termination bit if it happens to be set.
 200          */
 201         prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
 202 }
 203
 204 /**
 205  * sg_mark_end - Mark the end of the scatterlist
 206  * @sg:          SG entryScatterlist
 207  *
 208  * Description:
 209  *   Marks the passed in sg entry as the termination point for the sg
 210  *   table. A call to sg_next() on this entry will return NULL.
 211  *
 212  **/
 213 static inline void sg_mark_end(struct scatterlist *sg)
 214 {
 215 #ifdef CONFIG_DEBUG_SG
 216         BUG_ON(sg->sg_magic != SG_MAGIC);
 217 #endif
 218         /*
 219          * Set termination bit, clear potential chain bit
 220          */
 221         sg->page_link |= 0x02;
 222         sg->page_link &= ~0x01;
 223 }
 224
 225 /**
 226  * sg_init_table - Initialize SG table
 227  * @sgl:           The SG table
 228  * @nents:         Number of entries in table
 229  *
 230  * Notes:
 231  *   If this is part of a chained sg table, sg_mark_end() should be
 232  *   used only on the last table part.
 233  *
 234  **/
 235 static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
 236 {
 237         memset(sgl, 0, sizeof(*sgl) * nents);
 238 #ifdef CONFIG_DEBUG_SG
 239         {
 240                 unsigned int i;
 241                 for (i = 0; i < nents; i++)
 242                         sgl[i].sg_magic = SG_MAGIC;
 243         }
 244 #endif
 245         sg_mark_end(&sgl[nents - 1]);
 246 }
 247
 248 /**
 249  * sg_init_one - Initialize a single entry sg list
 250  * @sg:          SG entry
 251  * @buf:         Virtual address for IO
 252  * @buflen:      IO length
 253  *
 254  * Notes:
 255  *   This should not be used on a single entry that is part of a larger
 256  *   table. Use sg_init_table() for that.
 257  *
 258  **/
 259 static inline void sg_init_one(struct scatterlist *sg, const void *buf,
 260                                unsigned int buflen)
 261 {
 262         sg_init_table(sg, 1);
 263         sg_set_buf(sg, buf, buflen);
 264 }
 265
 266 /**
 267  * sg_phys - Return physical address of an sg entry
 268  * @sg:      SG entry
 269  *
 270  * Description:
 271  *   This calls page_to_phys() on the page in this sg entry, and adds the
 272  *   sg offset. The caller must know that it is legal to call page_to_phys()
 273  *   on the sg page.
 274  *
 275  **/
 276 static inline dma_addr_t sg_phys(struct scatterlist *sg)
 277 {
 278         return page_to_phys(sg_page(sg)) + sg->offset;
 279 }
 280
 281 /**
 282  * sg_virt - Return virtual address of an sg entry
 283  * @sg:      SG entry
 284  *
 285  * Description:
 286  *   This calls page_address() on the page in this sg entry, and adds the
 287  *   sg offset. The caller must know that the sg page has a valid virtual
 288  *   mapping.
 289  *
 290  **/
 291 static inline void *sg_virt(struct scatterlist *sg)
 292 {
 293         return page_address(sg_page(sg)) + sg->offset;
 294 }
 295
 296 #endif /* _LINUX_SCATTERLIST_H */