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 struct sg_table {
  11         struct scatterlist *sgl;        /* the list */
  12         unsigned int nents;             /* number of mapped entries */
  13         unsigned int orig_nents;        /* original size of list */
  14 };
  15
  16 /*
  17  * Notes on SG table design.
  18  *
  19  * Architectures must provide an unsigned long page_link field in the
  20  * scatterlist struct. We use that to place the page pointer AND encode
  21  * information about the sg table as well. The two lower bits are reserved
  22  * for this information.
  23  *
  24  * If bit 0 is set, then the page_link contains a pointer to the next sg
  25  * table list. Otherwise the next entry is at sg + 1.
  26  *
  27  * If bit 1 is set, then this sg entry is the last element in a list.
  28  *
  29  * See sg_next().
  30  *
  31  */
  32
  33 #define SG_MAGIC        0x87654321
  34
  35 /*
  36  * We overload the LSB of the page pointer to indicate whether it's
  37  * a valid sg entry, or whether it points to the start of a new scatterlist.
  38  * Those low bits are there for everyone! (thanks mason :-)
  39  */
  40 #define sg_is_chain(sg)         ((sg)->page_link & 0x01)
  41 #define sg_is_last(sg)          ((sg)->page_link & 0x02)
  42 #define sg_chain_ptr(sg)        \
  43         ((struct scatterlist *) ((sg)->page_link & ~0x03))
  44
  45 /**
  46  * sg_assign_page - Assign a given page to an SG entry
  47  * @sg:             SG entry
  48  * @page:           The page
  49  *
  50  * Description:
  51  *   Assign page to sg entry. Also see sg_set_page(), the most commonly used
  52  *   variant.
  53  *
  54  **/
  55 static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
  56 {
  57         unsigned long page_link = sg->page_link & 0x3;
  58
  59         /*
  60          * In order for the low bit stealing approach to work, pages
  61          * must be aligned at a 32-bit boundary as a minimum.
  62          */
  63         BUG_ON((unsigned long) page & 0x03);
  64 #ifdef CONFIG_DEBUG_SG
  65         BUG_ON(sg->sg_magic != SG_MAGIC);
  66         BUG_ON(sg_is_chain(sg));
  67 #endif
  68         sg->page_link = page_link | (unsigned long) page;
  69 }
  70
  71 /**
  72  * sg_set_page - Set sg entry to point at given page
  73  * @sg:          SG entry
  74  * @page:        The page
  75  * @len:         Length of data
  76  * @offset:      Offset into page
  77  *
  78  * Description:
  79  *   Use this function to set an sg entry pointing at a page, never assign
  80  *   the page directly. We encode sg table information in the lower bits
  81  *   of the page pointer. See sg_page() for looking up the page belonging
  82  *   to an sg entry.
  83  *
  84  **/
  85 static inline void sg_set_page(struct scatterlist *sg, struct page *page,
  86                                unsigned int len, unsigned int offset)
  87 {
  88         sg_assign_page(sg, page);
  89         sg->offset = offset;
  90         sg->length = len;
  91 }
  92
  93 static inline struct page *sg_page(struct scatterlist *sg)
  94 {
  95 #ifdef CONFIG_DEBUG_SG
  96         BUG_ON(sg->sg_magic != SG_MAGIC);
  97         BUG_ON(sg_is_chain(sg));
  98 #endif
  99         return (struct page *)((sg)->page_link & ~0x3);
 100 }
 101
 102 /**
 103  * sg_set_buf - Set sg entry to point at given data
 104  * @sg:          SG entry
 105  * @buf:         Data
 106  * @buflen:      Data length
 107  *
 108  **/
 109 static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
 110                               unsigned int buflen)
 111 {
 112         sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
 113 }
 114
 115 /*
 116  * Loop over each sg element, following the pointer to a new list if necessary
 117  */
 118 #define for_each_sg(sglist, sg, nr, __i)        \
 119         for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
 120
 121 /**
 122  * sg_chain - Chain two sglists together
 123  * @prv:        First scatterlist
 124  * @prv_nents:  Number of entries in prv
 125  * @sgl:        Second scatterlist
 126  *
 127  * Description:
 128  *   Links @prv@ and @sgl@ together, to form a longer scatterlist.
 129  *
 130  **/
 131 static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
 132                             struct scatterlist *sgl)
 133 {
 134 #ifndef ARCH_HAS_SG_CHAIN
 135         BUG();
 136 #endif
 137
 138         /*
 139          * offset and length are unused for chain entry.  Clear them.
 140          */
 141         prv[prv_nents - 1].offset = 0;
 142         prv[prv_nents - 1].length = 0;
 143
 144         /*
 145          * Set lowest bit to indicate a link pointer, and make sure to clear
 146          * the termination bit if it happens to be set.
 147          */
 148         prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
 149 }
 150
 151 /**
 152  * sg_mark_end - Mark the end of the scatterlist
 153  * @sg:          SG entryScatterlist
 154  *
 155  * Description:
 156  *   Marks the passed in sg entry as the termination point for the sg
 157  *   table. A call to sg_next() on this entry will return NULL.
 158  *
 159  **/
 160 static inline void sg_mark_end(struct scatterlist *sg)
 161 {
 162 #ifdef CONFIG_DEBUG_SG
 163         BUG_ON(sg->sg_magic != SG_MAGIC);
 164 #endif
 165         /*
 166          * Set termination bit, clear potential chain bit
 167          */
 168         sg->page_link |= 0x02;
 169         sg->page_link &= ~0x01;
 170 }
 171
 172 /**
 173  * sg_phys - Return physical address of an sg entry
 174  * @sg:      SG entry
 175  *
 176  * Description:
 177  *   This calls page_to_phys() on the page in this sg entry, and adds the
 178  *   sg offset. The caller must know that it is legal to call page_to_phys()
 179  *   on the sg page.
 180  *
 181  **/
 182 static inline dma_addr_t sg_phys(struct scatterlist *sg)
 183 {
 184         return page_to_phys(sg_page(sg)) + sg->offset;
 185 }
 186
 187 /**
 188  * sg_virt - Return virtual address of an sg entry
 189  * @sg:      SG entry
 190  *
 191  * Description:
 192  *   This calls page_address() on the page in this sg entry, and adds the
 193  *   sg offset. The caller must know that the sg page has a valid virtual
 194  *   mapping.
 195  *
 196  **/
 197 static inline void *sg_virt(struct scatterlist *sg)
 198 {
 199         return page_address(sg_page(sg)) + sg->offset;
 200 }
 201
 202 struct scatterlist *sg_next(struct scatterlist *);
 203 struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
 204 void sg_init_table(struct scatterlist *, unsigned int);
 205 void sg_init_one(struct scatterlist *, const void *, unsigned int);
 206
 207 typedef struct scatterlist *(sg_alloc_fn)(unsigned int, gfp_t);
 208 typedef void (sg_free_fn)(struct scatterlist *, unsigned int);
 209
 210 void __sg_free_table(struct sg_table *, unsigned int, sg_free_fn *);
 211 void sg_free_table(struct sg_table *);
 212 int __sg_alloc_table(struct sg_table *, unsigned int, unsigned int, gfp_t,
 213                      sg_alloc_fn *);
 214 int sg_alloc_table(struct sg_table *, unsigned int, gfp_t);
 215
 216 /*
 217  * Maximum number of entries that will be allocated in one piece, if
 218  * a list larger than this is required then chaining will be utilized.
 219  */
 220 #define SG_MAX_SINGLE_ALLOC             (PAGE_SIZE / sizeof(struct scatterlist))
 221
 222 #endif /* _LINUX_SCATTERLIST_H */