tools/virtio/linux/scatterlist.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef SCATTERLIST_H
   3 #define SCATTERLIST_H
   4 #include <linux/kernel.h>
   5
   6 struct scatterlist {
   7         unsigned long   page_link;
   8         unsigned int    offset;
   9         unsigned int    length;
  10         dma_addr_t      dma_address;
  11 };
  12
  13 /* Scatterlist helpers, stolen from linux/scatterlist.h */
  14 #define sg_is_chain(sg)         ((sg)->page_link & 0x01)
  15 #define sg_is_last(sg)          ((sg)->page_link & 0x02)
  16 #define sg_chain_ptr(sg)        \
  17         ((struct scatterlist *) ((sg)->page_link & ~0x03))
  18
  19 /**
  20  * sg_assign_page - Assign a given page to an SG entry
  21  * @sg:             SG entry
  22  * @page:           The page
  23  *
  24  * Description:
  25  *   Assign page to sg entry. Also see sg_set_page(), the most commonly used
  26  *   variant.
  27  *
  28  **/
  29 static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
  30 {
  31         unsigned long page_link = sg->page_link & 0x3;
  32
  33         /*
  34          * In order for the low bit stealing approach to work, pages
  35          * must be aligned at a 32-bit boundary as a minimum.
  36          */
  37         BUG_ON((unsigned long) page & 0x03);
  38 #ifdef CONFIG_DEBUG_SG
  39         BUG_ON(sg->sg_magic != SG_MAGIC);
  40         BUG_ON(sg_is_chain(sg));
  41 #endif
  42         sg->page_link = page_link | (unsigned long) page;
  43 }
  44
  45 /**
  46  * sg_set_page - Set sg entry to point at given page
  47  * @sg:          SG entry
  48  * @page:        The page
  49  * @len:         Length of data
  50  * @offset:      Offset into page
  51  *
  52  * Description:
  53  *   Use this function to set an sg entry pointing at a page, never assign
  54  *   the page directly. We encode sg table information in the lower bits
  55  *   of the page pointer. See sg_page() for looking up the page belonging
  56  *   to an sg entry.
  57  *
  58  **/
  59 static inline void sg_set_page(struct scatterlist *sg, struct page *page,
  60                                unsigned int len, unsigned int offset)
  61 {
  62         sg_assign_page(sg, page);
  63         sg->offset = offset;
  64         sg->length = len;
  65 }
  66
  67 static inline struct page *sg_page(struct scatterlist *sg)
  68 {
  69 #ifdef CONFIG_DEBUG_SG
  70         BUG_ON(sg->sg_magic != SG_MAGIC);
  71         BUG_ON(sg_is_chain(sg));
  72 #endif
  73         return (struct page *)((sg)->page_link & ~0x3);
  74 }
  75
  76 /*
  77  * Loop over each sg element, following the pointer to a new list if necessary
  78  */
  79 #define for_each_sg(sglist, sg, nr, __i)        \
  80         for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
  81
  82 /**
  83  * sg_chain - Chain two sglists together
  84  * @prv:        First scatterlist
  85  * @prv_nents:  Number of entries in prv
  86  * @sgl:        Second scatterlist
  87  *
  88  * Description:
  89  *   Links @prv@ and @sgl@ together, to form a longer scatterlist.
  90  *
  91  **/
  92 static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
  93                             struct scatterlist *sgl)
  94 {
  95         /*
  96          * offset and length are unused for chain entry.  Clear them.
  97          */
  98         prv[prv_nents - 1].offset = 0;
  99         prv[prv_nents - 1].length = 0;
 100
 101         /*
 102          * Set lowest bit to indicate a link pointer, and make sure to clear
 103          * the termination bit if it happens to be set.
 104          */
 105         prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
 106 }
 107
 108 /**
 109  * sg_mark_end - Mark the end of the scatterlist
 110  * @sg:          SG entryScatterlist
 111  *
 112  * Description:
 113  *   Marks the passed in sg entry as the termination point for the sg
 114  *   table. A call to sg_next() on this entry will return NULL.
 115  *
 116  **/
 117 static inline void sg_mark_end(struct scatterlist *sg)
 118 {
 119 #ifdef CONFIG_DEBUG_SG
 120         BUG_ON(sg->sg_magic != SG_MAGIC);
 121 #endif
 122         /*
 123          * Set termination bit, clear potential chain bit
 124          */
 125         sg->page_link |= 0x02;
 126         sg->page_link &= ~0x01;
 127 }
 128
 129 /**
 130  * sg_unmark_end - Undo setting the end of the scatterlist
 131  * @sg:          SG entryScatterlist
 132  *
 133  * Description:
 134  *   Removes the termination marker from the given entry of the scatterlist.
 135  *
 136  **/
 137 static inline void sg_unmark_end(struct scatterlist *sg)
 138 {
 139 #ifdef CONFIG_DEBUG_SG
 140         BUG_ON(sg->sg_magic != SG_MAGIC);
 141 #endif
 142         sg->page_link &= ~0x02;
 143 }
 144
 145 static inline struct scatterlist *sg_next(struct scatterlist *sg)
 146 {
 147 #ifdef CONFIG_DEBUG_SG
 148         BUG_ON(sg->sg_magic != SG_MAGIC);
 149 #endif
 150         if (sg_is_last(sg))
 151                 return NULL;
 152
 153         sg++;
 154         if (unlikely(sg_is_chain(sg)))
 155                 sg = sg_chain_ptr(sg);
 156
 157         return sg;
 158 }
 159
 160 static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
 161 {
 162         memset(sgl, 0, sizeof(*sgl) * nents);
 163 #ifdef CONFIG_DEBUG_SG
 164         {
 165                 unsigned int i;
 166                 for (i = 0; i < nents; i++)
 167                         sgl[i].sg_magic = SG_MAGIC;
 168         }
 169 #endif
 170         sg_mark_end(&sgl[nents - 1]);
 171 }
 172
 173 static inline dma_addr_t sg_phys(struct scatterlist *sg)
 174 {
 175         return page_to_phys(sg_page(sg)) + sg->offset;
 176 }
 177
 178 static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
 179                               unsigned int buflen)
 180 {
 181         sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
 182 }
 183
 184 static inline void sg_init_one(struct scatterlist *sg,
 185                                const void *buf, unsigned int buflen)
 186 {
 187         sg_init_table(sg, 1);
 188         sg_set_buf(sg, buf, buflen);
 189 }
 190 #endif /* SCATTERLIST_H */