#ifndef _LINUX_SCATTERLIST_H
  #define _LINUX_SCATTERLIST_H

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

  #include <asm/io.h>
  
  /*
   * 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

  /**

   * 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);
  #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;
  }

  #define sg_page(sg)	((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));

  }

  /*
   * 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_next - return the next scatterlist entry in a list
   * @sg:		The current sg entry
   *

   * Description:
   *   Usually the next entry will be @sg@ + 1, but if this sg element is part
   *   of a chained scatterlist, it could jump to the start of a new
   *   scatterlist array.

   *

   **/

  static inline struct scatterlist *sg_next(struct scatterlist *sg)
  {

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

  	if (sg_is_last(sg))
  		return NULL;

  	sg++;

  	if (unlikely(sg_is_chain(sg)))
  		sg = sg_chain_ptr(sg);
  
  	return sg;
  }

  
  /*
   * 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_last - return the last scatterlist entry in a list
   * @sgl:	First entry in the scatterlist
   * @nents:	Number of entries in the scatterlist
   *

   * Description:
   *   Should only be used casually, it (currently) scan the entire list
   *   to get the last entry.

   *

   *   Note that the @sgl@ pointer passed in need not be the first one,
   *   the important bit is that @nents@ denotes the number of entries that
   *   exist from @sgl@.

   *

   **/

  static inline struct scatterlist *sg_last(struct scatterlist *sgl,
  					  unsigned int nents)
  {
  #ifndef ARCH_HAS_SG_CHAIN
  	struct scatterlist *ret = &sgl[nents - 1];
  #else
  	struct scatterlist *sg, *ret = NULL;
  	int i;
  
  	for_each_sg(sgl, sg, nents, i)
  		ret = sg;
  
  #endif

  #ifdef CONFIG_DEBUG_SG
  	BUG_ON(sgl[0].sg_magic != SG_MAGIC);
  	BUG_ON(!sg_is_last(ret));
  #endif

  	return ret;
  }
  
  /**
   * 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

  	prv[prv_nents - 1].page_link = (unsigned long) sgl | 0x01;

  }

  /**
   * sg_mark_end - Mark the end of the scatterlist
   * @sgl:	Scatterlist
   * @nents:	Number of entries in sgl
   *
   * Description:
   *   Marks the last entry as the termination point for sg_next()
   *
   **/
  static inline void sg_mark_end(struct scatterlist *sgl, unsigned int nents)
  {

  	sgl[nents - 1].page_link = 0x02;

  }
  
  static inline void __sg_mark_end(struct scatterlist *sg)
  {

  	sg->page_link |= 0x02;

  }

  /**
   * sg_init_one - Initialize a single entry sg list
   * @sg:		 SG entry
   * @buf:	 Virtual address for IO
   * @buflen:	 IO length
   *
   * Notes:
   *   This should not be used on a single entry that is part of a larger
   *   table. Use sg_init_table() for that.
   *
   **/
  static inline void sg_init_one(struct scatterlist *sg, const void *buf,
  			       unsigned int buflen)
  {
  	memset(sg, 0, sizeof(*sg));

  #ifdef CONFIG_DEBUG_SG
  	sg->sg_magic = SG_MAGIC;
  #endif

  	sg_mark_end(sg, 1);
  	sg_set_buf(sg, buf, buflen);
  }
  
  /**
   * sg_init_table - Initialize SG table
   * @sgl:	   The SG table
   * @nents:	   Number of entries in table
   *
   * Notes:
   *   If this is part of a chained sg table, sg_mark_end() should be
   *   used only on the last table part.
   *
   **/
  static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
  {
  	memset(sgl, 0, sizeof(*sgl) * nents);
  	sg_mark_end(sgl, nents);

  #ifdef CONFIG_DEBUG_SG
  	{
  		int i;
  		for (i = 0; i < nents; i++)
  			sgl[i].sg_magic = SG_MAGIC;
  	}
  #endif

  }
  
  /**
   * 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 unsigned long 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;
  }

  #endif /* _LINUX_SCATTERLIST_H */