scatterlist.h

  1/* SPDX-License-Identifier: GPL-2.0 */
  2#ifndef SCATTERLIST_H
  3#define SCATTERLIST_H
  4#include <linux/kernel.h>
  5#include <linux/bug.h>
  6
  7struct scatterlist {
  8	unsigned long	page_link;
  9	unsigned int	offset;
 10	unsigned int	length;
 11	dma_addr_t	dma_address;
 12};
 13
 14/* Scatterlist helpers, stolen from linux/scatterlist.h */
 15#define sg_is_chain(sg)		((sg)->page_link & 0x01)
 16#define sg_is_last(sg)		((sg)->page_link & 0x02)
 17#define sg_chain_ptr(sg)	\
 18	((struct scatterlist *) ((sg)->page_link & ~0x03))
 19
 20/**
 21 * sg_assign_page - Assign a given page to an SG entry
 22 * @sg:		    SG entry
 23 * @page:	    The page
 24 *
 25 * Description:
 26 *   Assign page to sg entry. Also see sg_set_page(), the most commonly used
 27 *   variant.
 28 *
 29 **/
 30static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
 31{
 32	unsigned long page_link = sg->page_link & 0x3;
 33
 34	/*
 35	 * In order for the low bit stealing approach to work, pages
 36	 * must be aligned at a 32-bit boundary as a minimum.
 37	 */
 38	BUG_ON((unsigned long) page & 0x03);
 39#ifdef CONFIG_DEBUG_SG
 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 **/
 59static 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
 67static inline struct page *sg_page(struct scatterlist *sg)
 68{
 69#ifdef CONFIG_DEBUG_SG
 70	BUG_ON(sg_is_chain(sg));
 71#endif
 72	return (struct page *)((sg)->page_link & ~0x3);
 73}
 74
 75/*
 76 * Loop over each sg element, following the pointer to a new list if necessary
 77 */
 78#define for_each_sg(sglist, sg, nr, __i)	\
 79	for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
 80
 81/**
 82 * sg_chain - Chain two sglists together
 83 * @prv:	First scatterlist
 84 * @prv_nents:	Number of entries in prv
 85 * @sgl:	Second scatterlist
 86 *
 87 * Description:
 88 *   Links @prv@ and @sgl@ together, to form a longer scatterlist.
 89 *
 90 **/
 91static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
 92			    struct scatterlist *sgl)
 93{
 94	/*
 95	 * offset and length are unused for chain entry.  Clear them.
 96	 */
 97	prv[prv_nents - 1].offset = 0;
 98	prv[prv_nents - 1].length = 0;
 99
100	/*
101	 * Set lowest bit to indicate a link pointer, and make sure to clear
102	 * the termination bit if it happens to be set.
103	 */
104	prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
105}
106
107/**
108 * sg_mark_end - Mark the end of the scatterlist
109 * @sg:		 SG entryScatterlist
110 *
111 * Description:
112 *   Marks the passed in sg entry as the termination point for the sg
113 *   table. A call to sg_next() on this entry will return NULL.
114 *
115 **/
116static inline void sg_mark_end(struct scatterlist *sg)
117{
118	/*
119	 * Set termination bit, clear potential chain bit
120	 */
121	sg->page_link |= 0x02;
122	sg->page_link &= ~0x01;
123}
124
125/**
126 * sg_unmark_end - Undo setting the end of the scatterlist
127 * @sg:		 SG entryScatterlist
128 *
129 * Description:
130 *   Removes the termination marker from the given entry of the scatterlist.
131 *
132 **/
133static inline void sg_unmark_end(struct scatterlist *sg)
134{
135	sg->page_link &= ~0x02;
136}
137
138static inline struct scatterlist *sg_next(struct scatterlist *sg)
139{
140	if (sg_is_last(sg))
141		return NULL;
142
143	sg++;
144	if (unlikely(sg_is_chain(sg)))
145		sg = sg_chain_ptr(sg);
146
147	return sg;
148}
149
150static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
151{
152	memset(sgl, 0, sizeof(*sgl) * nents);
153	sg_mark_end(&sgl[nents - 1]);
154}
155
156static inline dma_addr_t sg_phys(struct scatterlist *sg)
157{
158	return page_to_phys(sg_page(sg)) + sg->offset;
159}
160
161static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
162			      unsigned int buflen)
163{
164	sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
165}
166
167static inline void sg_init_one(struct scatterlist *sg,
168			       const void *buf, unsigned int buflen)
169{
170	sg_init_table(sg, 1);
171	sg_set_buf(sg, buf, buflen);
172}
173#endif /* SCATTERLIST_H */