1 /*
2 * Example showing how to pin down a range of virtual pages from user-space
3 * to be able to do for example DMA directly into them.
4 *
5 * It is necessary because the pages the virtual pointers reference, might
6 * not exist in memory (could be mapped to the zero-page, filemapped etc)
7 * and DMA cannot trigger the MMU to force them in (and would have time
8 * contraints making it impossible to wait for it anyway).
9 *
10 * Copyright (c) 2001, 2002, 2003 Axis Communications AB
11 *
12 * Author: Bjorn Wesen
13 *
14 */
15
16 #include <linux/module.h>
17 #include <linux/sched.h>
18 #include <linux/slab.h>
19 #include <linux/errno.h>
20 #include <linux/kernel.h>
21 #include <linux/fs.h>
22 #include <linux/string.h>
23 #include <linux/init.h>
24 #include <linux/mm.h>
25 #include <linux/iobuf.h>
26
27 #define KIOBUFTEST_MAJOR 124 /* in the local range, experimental */
28
29 static ssize_t
kiobuf_read(struct file * filp,char * buf,size_t len,loff_t * ppos)30 kiobuf_read(struct file *filp, char *buf, size_t len, loff_t *ppos)
31 {
32 struct kiobuf *iobuf;
33 int res, i;
34
35 /*
36 * Make a kiobuf that maps the entire length the reader has given us.
37 */
38
39 res = alloc_kiovec(1, &iobuf);
40 if (res)
41 return res;
42
43 if ((res = map_user_kiobuf(READ, iobuf, (unsigned long)buf, len))) {
44 printk("map_user_kiobuf failed, return %d\n", res);
45 free_kiovec(1, &iobuf);
46 return res;
47 }
48
49 /*
50 * At this point, the virtual area buf[0] -> buf[len-1] will have
51 * corresponding pages mapped in physical memory and locked until
52 * we unmap the kiobuf. They cannot be swapped out or moved around.
53 */
54
55 printk("nr_pages == %d\noffset == %d\nlength == %d\n",
56 iobuf->nr_pages, iobuf->offset, iobuf->length);
57
58 for (i = 0; i < iobuf->nr_pages; i++) {
59 printk("page_add(maplist[%d]) == 0x%x\n", i,
60 page_address(iobuf->maplist[i]));
61 }
62
63 /*
64 * This is the place to create the necessary scatter-gather vector
65 * for the DMA using the iobuf->maplist array and page_address (don't
66 * forget __pa if the DMA needs the actual physical DRAM address)
67 * and run it.
68 */
69
70
71
72 /* Release the mapping and exit */
73
74 unmap_kiobuf(iobuf); /* The unlock_kiobuf is implicit here */
75 free_kiovec(1, &iobuf);
76
77 return len;
78 }
79
80
81 static struct file_operations kiobuf_fops = {
82 owner: THIS_MODULE,
83 read: kiobuf_read
84 };
85
86 static int __init
kiobuftest_init(void)87 kiobuftest_init(void)
88 {
89 int res;
90
91 /* register char device */
92
93 res = register_chrdev(KIOBUFTEST_MAJOR, "kiobuftest", &kiobuf_fops);
94 if (res < 0) {
95 printk(KERN_ERR "kiobuftest: couldn't get a major number.\n");
96 return res;
97 }
98
99 printk("Initializing kiobuf-test device\n");
100 }
101
102 static void __exit
kiobuftest_exit(void)103 kiobuftest_exit(void)
104 {
105 unregister_chrdev(KIOBUFTEST_MAJOR, "kiobuftest");
106 }
107
108 module_init(kiobuftest_init);
109 module_exit(kiobuftest_exit);
110