virtio/linux/scatterlist.h

0001 /* SPDX-License-Identifier: GPL-2.0 */
0002 #ifndef SCATTERLIST_H
0003 #define SCATTERLIST_H
0004 #include <linux/kernel.h>
0005
0006 struct scatterlist {
0007     unsigned long   page_link;
0008     unsigned int    offset;
0009     unsigned int    length;
0010     dma_addr_t  dma_address;
0011 };
0012
0013 /* Scatterlist helpers, stolen from linux/scatterlist.h */
0014 #define sg_is_chain(sg)     ((sg)->page_link & 0x01)
0015 #define sg_is_last(sg)      ((sg)->page_link & 0x02)
0016 #define sg_chain_ptr(sg)    \
0017     ((struct scatterlist *) ((sg)->page_link & ~0x03))
0018
0019 /**
0020  * sg_assign_page - Assign a given page to an SG entry
0021  * @sg:         SG entry
0022  * @page:       The page
0023  *
0024  * Description:
0025  *   Assign page to sg entry. Also see sg_set_page(), the most commonly used
0026  *   variant.
0027  *
0028  **/
0029 static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
0030 {
0031     unsigned long page_link = sg->page_link & 0x3;
0032
0033     /*
0034      * In order for the low bit stealing approach to work, pages
0035      * must be aligned at a 32-bit boundary as a minimum.
0036      */
0037     BUG_ON((unsigned long) page & 0x03);
0038 #ifdef CONFIG_DEBUG_SG
0039     BUG_ON(sg_is_chain(sg));
0040 #endif
0041     sg->page_link = page_link | (unsigned long) page;
0042 }
0043
0044 /**
0045  * sg_set_page - Set sg entry to point at given page
0046  * @sg:      SG entry
0047  * @page:    The page
0048  * @len:     Length of data
0049  * @offset:  Offset into page
0050  *
0051  * Description:
0052  *   Use this function to set an sg entry pointing at a page, never assign
0053  *   the page directly. We encode sg table information in the lower bits
0054  *   of the page pointer. See sg_page() for looking up the page belonging
0055  *   to an sg entry.
0056  *
0057  **/
0058 static inline void sg_set_page(struct scatterlist *sg, struct page *page,
0059                    unsigned int len, unsigned int offset)
0060 {
0061     sg_assign_page(sg, page);
0062     sg->offset = offset;
0063     sg->length = len;
0064 }
0065
0066 static inline struct page *sg_page(struct scatterlist *sg)
0067 {
0068 #ifdef CONFIG_DEBUG_SG
0069     BUG_ON(sg_is_chain(sg));
0070 #endif
0071     return (struct page *)((sg)->page_link & ~0x3);
0072 }
0073
0074 /*
0075  * Loop over each sg element, following the pointer to a new list if necessary
0076  */
0077 #define for_each_sg(sglist, sg, nr, __i)    \
0078     for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
0079
0080 /**
0081  * sg_chain - Chain two sglists together
0082  * @prv:    First scatterlist
0083  * @prv_nents:  Number of entries in prv
0084  * @sgl:    Second scatterlist
0085  *
0086  * Description:
0087  *   Links @prv@ and @sgl@ together, to form a longer scatterlist.
0088  *
0089  **/
0090 static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
0091                 struct scatterlist *sgl)
0092 {
0093     /*
0094      * offset and length are unused for chain entry.  Clear them.
0095      */
0096     prv[prv_nents - 1].offset = 0;
0097     prv[prv_nents - 1].length = 0;
0098
0099     /*
0100      * Set lowest bit to indicate a link pointer, and make sure to clear
0101      * the termination bit if it happens to be set.
0102      */
0103     prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
0104 }
0105
0106 /**
0107  * sg_mark_end - Mark the end of the scatterlist
0108  * @sg:      SG entryScatterlist
0109  *
0110  * Description:
0111  *   Marks the passed in sg entry as the termination point for the sg
0112  *   table. A call to sg_next() on this entry will return NULL.
0113  *
0114  **/
0115 static inline void sg_mark_end(struct scatterlist *sg)
0116 {
0117     /*
0118      * Set termination bit, clear potential chain bit
0119      */
0120     sg->page_link |= 0x02;
0121     sg->page_link &= ~0x01;
0122 }
0123
0124 /**
0125  * sg_unmark_end - Undo setting the end of the scatterlist
0126  * @sg:      SG entryScatterlist
0127  *
0128  * Description:
0129  *   Removes the termination marker from the given entry of the scatterlist.
0130  *
0131  **/
0132 static inline void sg_unmark_end(struct scatterlist *sg)
0133 {
0134     sg->page_link &= ~0x02;
0135 }
0136
0137 static inline struct scatterlist *sg_next(struct scatterlist *sg)
0138 {
0139     if (sg_is_last(sg))
0140         return NULL;
0141
0142     sg++;
0143     if (unlikely(sg_is_chain(sg)))
0144         sg = sg_chain_ptr(sg);
0145
0146     return sg;
0147 }
0148
0149 static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
0150 {
0151     memset(sgl, 0, sizeof(*sgl) * nents);
0152     sg_mark_end(&sgl[nents - 1]);
0153 }
0154
0155 static inline dma_addr_t sg_phys(struct scatterlist *sg)
0156 {
0157     return page_to_phys(sg_page(sg)) + sg->offset;
0158 }
0159
0160 static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
0161                   unsigned int buflen)
0162 {
0163     sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
0164 }
0165
0166 static inline void sg_init_one(struct scatterlist *sg,
0167                    const void *buf, unsigned int buflen)
0168 {
0169     sg_init_table(sg, 1);
0170     sg_set_buf(sg, buf, buflen);
0171 }
0172 #endif /* SCATTERLIST_H */