#ifndef _LINUX_SCATTERLIST_H
  #define _LINUX_SCATTERLIST_H

  #include <asm/types.h>

  #include <asm/scatterlist.h>
  #include <linux/mm.h>
  #include <linux/string.h>

  #include <asm/io.h>

  struct sg_table {
  	struct scatterlist *sgl;	/* the list */
  	unsigned int nents;		/* number of mapped entries */
  	unsigned int orig_nents;	/* original size of list */
  };

  /*
   * Notes on SG table design.
   *
   * Architectures must provide an unsigned long page_link field in the
   * scatterlist struct. We use that to place the page pointer AND encode
   * information about the sg table as well. The two lower bits are reserved
   * for this information.
   *
   * If bit 0 is set, then the page_link contains a pointer to the next sg
   * table list. Otherwise the next entry is at sg + 1.
   *
   * If bit 1 is set, then this sg entry is the last element in a list.
   *
   * See sg_next().
   *
   */

  #define SG_MAGIC	0x87654321

  /*
   * We overload the LSB of the page pointer to indicate whether it's
   * a valid sg entry, or whether it points to the start of a new scatterlist.
   * Those low bits are there for everyone! (thanks mason :-)
   */
  #define sg_is_chain(sg)		((sg)->page_link & 0x01)
  #define sg_is_last(sg)		((sg)->page_link & 0x02)
  #define sg_chain_ptr(sg)	\
  	((struct scatterlist *) ((sg)->page_link & ~0x03))

  /**

   * sg_assign_page - Assign a given page to an SG entry
   * @sg:		    SG entry
   * @page:	    The page

   *
   * Description:

   *   Assign page to sg entry. Also see sg_set_page(), the most commonly used
   *   variant.

   *
   **/

  static inline void sg_assign_page(struct scatterlist *sg, struct page *page)

  {

  	unsigned long page_link = sg->page_link & 0x3;

  	/*
  	 * In order for the low bit stealing approach to work, pages
  	 * must be aligned at a 32-bit boundary as a minimum.
  	 */
  	BUG_ON((unsigned long) page & 0x03);

  #ifdef CONFIG_DEBUG_SG
  	BUG_ON(sg->sg_magic != SG_MAGIC);

  	BUG_ON(sg_is_chain(sg));

  #endif

  	sg->page_link = page_link | (unsigned long) page;

  }

  /**
   * sg_set_page - Set sg entry to point at given page
   * @sg:		 SG entry
   * @page:	 The page
   * @len:	 Length of data
   * @offset:	 Offset into page
   *
   * Description:
   *   Use this function to set an sg entry pointing at a page, never assign
   *   the page directly. We encode sg table information in the lower bits
   *   of the page pointer. See sg_page() for looking up the page belonging
   *   to an sg entry.
   *
   **/
  static inline void sg_set_page(struct scatterlist *sg, struct page *page,
  			       unsigned int len, unsigned int offset)
  {
  	sg_assign_page(sg, page);
  	sg->offset = offset;
  	sg->length = len;
  }

  static inline struct page *sg_page(struct scatterlist *sg)
  {
  #ifdef CONFIG_DEBUG_SG
  	BUG_ON(sg->sg_magic != SG_MAGIC);
  	BUG_ON(sg_is_chain(sg));
  #endif
  	return (struct page *)((sg)->page_link & ~0x3);
  }

  /**
   * sg_set_buf - Set sg entry to point at given data
   * @sg:		 SG entry
   * @buf:	 Data
   * @buflen:	 Data length
   *
   **/

  static inline void sg_set_buf(struct scatterlist *sg, const void *buf,

  			      unsigned int buflen)
  {

  	sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));

  }

  /*
   * Loop over each sg element, following the pointer to a new list if necessary
   */
  #define for_each_sg(sglist, sg, nr, __i)	\
  	for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))

  /**

   * sg_chain - Chain two sglists together
   * @prv:	First scatterlist
   * @prv_nents:	Number of entries in prv
   * @sgl:	Second scatterlist
   *

   * Description:
   *   Links @prv@ and @sgl@ together, to form a longer scatterlist.

   *

   **/

  static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
  			    struct scatterlist *sgl)
  {
  #ifndef ARCH_HAS_SG_CHAIN
  	BUG();
  #endif

  
  	/*
  	 * offset and length are unused for chain entry.  Clear them.
  	 */

  	prv[prv_nents - 1].offset = 0;
  	prv[prv_nents - 1].length = 0;

  	/*
  	 * Set lowest bit to indicate a link pointer, and make sure to clear
  	 * the termination bit if it happens to be set.
  	 */
  	prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;

  }

  /**
   * sg_mark_end - Mark the end of the scatterlist

   * @sg:		 SG entryScatterlist

   *
   * Description:

   *   Marks the passed in sg entry as the termination point for the sg
   *   table. A call to sg_next() on this entry will return NULL.

   *
   **/

  static inline void sg_mark_end(struct scatterlist *sg)

  {

  #ifdef CONFIG_DEBUG_SG
  	BUG_ON(sg->sg_magic != SG_MAGIC);
  #endif
  	/*
  	 * Set termination bit, clear potential chain bit
  	 */

  	sg->page_link |= 0x02;

  	sg->page_link &= ~0x01;

  }

  /**

   * sg_phys - Return physical address of an sg entry
   * @sg:	     SG entry
   *
   * Description:
   *   This calls page_to_phys() on the page in this sg entry, and adds the
   *   sg offset. The caller must know that it is legal to call page_to_phys()
   *   on the sg page.
   *
   **/

  static inline dma_addr_t sg_phys(struct scatterlist *sg)

  {
  	return page_to_phys(sg_page(sg)) + sg->offset;
  }
  
  /**
   * sg_virt - Return virtual address of an sg entry

   * @sg:      SG entry

   *
   * Description:
   *   This calls page_address() on the page in this sg entry, and adds the
   *   sg offset. The caller must know that the sg page has a valid virtual
   *   mapping.
   *
   **/
  static inline void *sg_virt(struct scatterlist *sg)
  {
  	return page_address(sg_page(sg)) + sg->offset;
  }

  struct scatterlist *sg_next(struct scatterlist *);
  struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
  void sg_init_table(struct scatterlist *, unsigned int);
  void sg_init_one(struct scatterlist *, const void *, unsigned int);
  
  typedef struct scatterlist *(sg_alloc_fn)(unsigned int, gfp_t);
  typedef void (sg_free_fn)(struct scatterlist *, unsigned int);

  void __sg_free_table(struct sg_table *, unsigned int, sg_free_fn *);

  void sg_free_table(struct sg_table *);

  int __sg_alloc_table(struct sg_table *, unsigned int, unsigned int, gfp_t,
  		     sg_alloc_fn *);

  int sg_alloc_table(struct sg_table *, unsigned int, gfp_t);

  size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
  			   void *buf, size_t buflen);
  size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
  			 void *buf, size_t buflen);

  /*
   * Maximum number of entries that will be allocated in one piece, if
   * a list larger than this is required then chaining will be utilized.
   */
  #define SG_MAX_SINGLE_ALLOC		(PAGE_SIZE / sizeof(struct scatterlist))

  
  /*
   * Mapping sg iterator
   *
   * Iterates over sg entries mapping page-by-page.  On each successful
   * iteration, @miter->page points to the mapped page and
   * @miter->length bytes of data can be accessed at @miter->addr.  As
   * long as an interation is enclosed between start and stop, the user
   * is free to choose control structure and when to stop.
   *
   * @miter->consumed is set to @miter->length on each iteration.  It
   * can be adjusted if the user can't consume all the bytes in one go.
   * Also, a stopped iteration can be resumed by calling next on it.
   * This is useful when iteration needs to release all resources and
   * continue later (e.g. at the next interrupt).
   */
  
  #define SG_MITER_ATOMIC		(1 << 0)	 /* use kmap_atomic */
  
  struct sg_mapping_iter {
  	/* the following three fields can be accessed directly */
  	struct page		*page;		/* currently mapped page */
  	void			*addr;		/* pointer to the mapped area */
  	size_t			length;		/* length of the mapped area */
  	size_t			consumed;	/* number of consumed bytes */
  
  	/* these are internal states, keep away */
  	struct scatterlist	*__sg;		/* current entry */
  	unsigned int		__nents;	/* nr of remaining entries */
  	unsigned int		__offset;	/* offset within sg */
  	unsigned int		__flags;
  };
  
  void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
  		    unsigned int nents, unsigned int flags);
  bool sg_miter_next(struct sg_mapping_iter *miter);
  void sg_miter_stop(struct sg_mapping_iter *miter);

  #endif /* _LINUX_SCATTERLIST_H */