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linux/include/asm-frv/scatterlist.h
Jens Axboe 18dabf473e Change table chaining layout
Change the page member of the scatterlist structure to be an unsigned
long, and encode more stuff in the lower bits:

- Bits 0 and 1 zero: this is a normal sg entry. Next sg entry is located
  at sg + 1.
- Bit 0 set: this is a chain entry, the next real entry is at ->page_link
  with the two low bits masked off.
- Bit 1 set: this is the final entry in the sg entry. sg_next() will return
  NULL when passed such an entry.

It's thus important that sg table users use the proper accessors to get
and set the page member.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-10-22 21:20:01 +02:00

35 lines
931 B
C

#ifndef _ASM_SCATTERLIST_H
#define _ASM_SCATTERLIST_H
#include <asm/types.h>
/*
* Drivers must set either ->address or (preferred) ->page and ->offset
* to indicate where data must be transferred to/from.
*
* Using ->page is recommended since it handles highmem data as well as
* low mem. ->address is restricted to data which has a virtual mapping, and
* it will go away in the future. Updating to ->page can be automated very
* easily -- something like
*
* sg->address = some_ptr;
*
* can be rewritten as
*
* sg->page = virt_to_page(some_ptr);
* sg->offset = (unsigned long) some_ptr & ~PAGE_MASK;
*
* and that's it. There's no excuse for not highmem enabling YOUR driver. /jens
*/
struct scatterlist {
unsigned long page_link;
unsigned int offset; /* for highmem, page offset */
dma_addr_t dma_address;
unsigned int length;
};
#define ISA_DMA_THRESHOLD (0xffffffffUL)
#endif /* !_ASM_SCATTERLIST_H */