map_absent.c revision 1f948b43f7b5cf721cf0d03f507843efc1a9bfad 
1/*
2 * Common code to handle absent "placeholder" devices
3 * Copyright 2001 Resilience Corporation <ebrower@resilience.com>
4 * $Id: map_absent.c,v 1.6 2005/11/07 11:14:23 gleixner Exp $
5 *
6 * This map driver is used to allocate "placeholder" MTD
7 * devices on systems that have socketed/removable media.
8 * Use of this driver as a fallback preserves the expected
9 * registration of MTD device nodes regardless of probe outcome.
10 * A usage example is as follows:
11 *
12 *		my_dev[i] = do_map_probe("cfi", &my_map[i]);
13 *		if(NULL == my_dev[i]) {
14 *			my_dev[i] = do_map_probe("map_absent", &my_map[i]);
15 *		}
16 *
17 * Any device 'probed' with this driver will return -ENODEV
18 * upon open.
19 */
20
21#include <linux/module.h>
22#include <linux/types.h>
23#include <linux/kernel.h>
24#include <linux/errno.h>
25#include <linux/slab.h>
26#include <linux/init.h>
27#include <linux/mtd/mtd.h>
28#include <linux/mtd/map.h>
29#include <linux/mtd/compatmac.h>
30
31static int map_absent_read (struct mtd_info *, loff_t, size_t, size_t *, u_char *);
32static int map_absent_write (struct mtd_info *, loff_t, size_t, size_t *, const u_char *);
33static int map_absent_erase (struct mtd_info *, struct erase_info *);
34static void map_absent_sync (struct mtd_info *);
35static struct mtd_info *map_absent_probe(struct map_info *map);
36static void map_absent_destroy (struct mtd_info *);
37
38
39static struct mtd_chip_driver map_absent_chipdrv = {
40	.probe		= map_absent_probe,
41	.destroy	= map_absent_destroy,
42	.name		= "map_absent",
43	.module		= THIS_MODULE
44};
45
46static struct mtd_info *map_absent_probe(struct map_info *map)
47{
48	struct mtd_info *mtd;
49
50	mtd = kmalloc(sizeof(*mtd), GFP_KERNEL);
51	if (!mtd) {
52		return NULL;
53	}
54
55	memset(mtd, 0, sizeof(*mtd));
56
57	map->fldrv 	= &map_absent_chipdrv;
58	mtd->priv 	= map;
59	mtd->name 	= map->name;
60	mtd->type 	= MTD_ABSENT;
61	mtd->size 	= map->size;
62	mtd->erase 	= map_absent_erase;
63	mtd->read 	= map_absent_read;
64	mtd->write 	= map_absent_write;
65	mtd->sync 	= map_absent_sync;
66	mtd->flags 	= 0;
67	mtd->erasesize = PAGE_SIZE;
68
69	__module_get(THIS_MODULE);
70	return mtd;
71}
72
73
74static int map_absent_read(struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen, u_char *buf)
75{
76	*retlen = 0;
77	return -ENODEV;
78}
79
80static int map_absent_write(struct mtd_info *mtd, loff_t to, size_t len, size_t *retlen, const u_char *buf)
81{
82	*retlen = 0;
83	return -ENODEV;
84}
85
86static int map_absent_erase(struct mtd_info *mtd, struct erase_info *instr)
87{
88	return -ENODEV;
89}
90
91static void map_absent_sync(struct mtd_info *mtd)
92{
93	/* nop */
94}
95
96static void map_absent_destroy(struct mtd_info *mtd)
97{
98	/* nop */
99}
100
101static int __init map_absent_init(void)
102{
103	register_mtd_chip_driver(&map_absent_chipdrv);
104	return 0;
105}
106
107static void __exit map_absent_exit(void)
108{
109	unregister_mtd_chip_driver(&map_absent_chipdrv);
110}
111
112module_init(map_absent_init);
113module_exit(map_absent_exit);
114
115MODULE_LICENSE("GPL");
116MODULE_AUTHOR("Resilience Corporation - Eric Brower <ebrower@resilience.com>");
117MODULE_DESCRIPTION("Placeholder MTD chip driver for 'absent' chips");
118