kiobuftest.c

自己根据lkd和情境分析

/*
 * Example showing how to pin down a range of virtual pages from user-space
 * to be able to do for example DMA directly into them.
 *
 * It is necessary because the pages the virtual pointers reference, might
 * not exist in memory (could be mapped to the zero-page, filemapped etc)
 * and DMA cannot trigger the MMU to force them in (and would have time 
 * contraints making it impossible to wait for it anyway).
 *
 * Author:  Bjorn Wesen
 *
 * $Log: kiobuftest.c,v $
 * Revision 1.1.1.1  2004/02/04 12:55:29  laputa
 * rel-1-0-0 laputa: s3c2410 smdk
 *                   - the file for default configuration is "arch/arm/def-configs/smdk2410"
 *                   - the default lcd controller is set the aiji board base
 *                   - if you need to support the meritech board you should be
 *                     changed aiji item off of menuconfig
 *
 * Revision 1.1.1.1  2004/01/14 04:41:38  laputa
 * dev-0-0-1 laputa: initial import of 2410 kernel 
 *                   - the file for default configuration is "arch/arm/def-configs/smdk2410"
 *                   - the default lcd controller is set the aiji board base
 *
 * Revision 1.2  2001/02/27 13:52:50  bjornw
 * malloc.h -> slab.h
 *
 * Revision 1.1  2001/01/19 15:57:49  bjornw
 * Example of how to do direct HW -> user-mode DMA
 *
 *
 */

#include <linux/module.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/iobuf.h>

#define KIOBUFTEST_MAJOR 124  /* in the local range, experimental */


static ssize_t
kiobuf_read(struct file *filp, char *buf, size_t len, loff_t *ppos)
{

     struct kiobuf *iobuf;
     int res, i;
 
     /* Make a kiobuf that maps the entire length the reader has given
      * us
      */

     res = alloc_kiovec(1, &iobuf);
     if (res)
	     return res;
     
     if((res = map_user_kiobuf(READ, iobuf, (unsigned long)buf, len))) {
	     printk("map_user_kiobuf failed, return %d\n", res);
	     return res;
     }

     /* At this point, the virtual area buf[0] -> buf[len-1] will
      * have corresponding pages mapped in physical memory and locked
      * until we unmap the kiobuf. They cannot be swapped out or moved
      * around.
      */

     printk("nr_pages == %d\noffset == %d\nlength == %d\n",
	    iobuf->nr_pages, iobuf->offset, iobuf->length);

     for(i = 0; i < iobuf->nr_pages; i++) {
	     printk("page_add(maplist[%d]) == 0x%x\n", i,
		    page_address(iobuf->maplist[i]));
     }

     /* This is the place to create the necessary scatter-gather vector
      * for the DMA using the iobuf->maplist array and page_address
      * (don't forget __pa if the DMA needs the actual physical DRAM address)
      * and run it.
      */




     /* Release the mapping and exit */

     unmap_kiobuf(iobuf); /* The unlock_kiobuf is implicit here */

     return len;
}


static struct file_operations kiobuf_fops = {
	owner:    THIS_MODULE,
	read:     kiobuf_read
};

static int __init
kiobuftest_init(void)
{
	int res;

	/* register char device */

	res = register_chrdev(KIOBUFTEST_MAJOR, "kiobuftest", &kiobuf_fops);
	if(res < 0) {
		printk(KERN_ERR "kiobuftest: couldn't get a major number.\n");
		return res;
	}

	printk("Initializing kiobuf-test device\n");
}

module_init(kiobuftest_init);