nvram.c revision 172998 
1/*-
2 * Copyright (c) 2007 Peter Wemm
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 * $FreeBSD: head/sys/dev/nvram/nvram.c 172998 2007-10-26 03:23:54Z peter $
27 */
28
29#include <sys/param.h>
30#include <sys/systm.h>
31#include <sys/kernel.h>
32#include <sys/conf.h>
33#include <sys/fcntl.h>
34#include <sys/proc.h>
35#include <sys/uio.h>
36#include <sys/module.h>
37
38#include <machine/clock.h>
39#include <isa/rtc.h>
40
41/*
42 * Linux-style /dev/nvram driver
43 *
44 * cmos ram starts at bytes 14 through 128, for a total of 114 bytes.
45 * The driver exposes byte 14 as file offset 0.
46 *
47 * Offsets 2 through 31 are checksummed at offset 32, 33.
48 * In order to avoid the possibility of making the machine unbootable at the
49 * bios level (press F1 to continue!), we refuse to allow writes if we do
50 * not see a pre-existing valid checksum.  If the existing sum is invalid,
51 * then presumably we do not know how to make a sum that the bios will accept.
52 */
53
54#define NVRAM_FIRST	RTC_DIAG	/* 14 */
55#define NVRAM_LAST	128
56
57#define CKSUM_FIRST	2
58#define CKSUM_LAST	31
59#define CKSUM_MSB	32
60#define CKSUM_LSB	33
61
62static d_open_t		nvram_open;
63static d_read_t		nvram_read;
64static d_write_t	nvram_write;
65
66static struct cdev *nvram_dev;
67
68static struct cdevsw nvram_cdevsw = {
69	.d_version =	D_VERSION,
70	.d_flags =	D_NEEDGIANT,
71	.d_open =	nvram_open,
72	.d_read =	nvram_read,
73	.d_write =	nvram_write,
74	.d_name =	"nvram",
75};
76
77static int
78nvram_open(struct cdev *dev __unused, int flags, int fmt __unused,
79    struct thread *td)
80{
81	int error = 0;
82
83	if (flags & FWRITE)
84		error = securelevel_gt(td->td_ucred, 0);
85
86	return (error);
87}
88
89static int
90nvram_read(struct cdev *dev, struct uio *uio, int flags)
91{
92	int nv_off;
93	u_char v;
94	int error = 0;
95
96	while (uio->uio_resid > 0 && error == 0) {
97		nv_off = uio->uio_offset + NVRAM_FIRST;
98		if (nv_off < NVRAM_FIRST || nv_off >= NVRAM_LAST)
99			return (0);	/* Signal EOF */
100		/* Single byte at a time */
101		v = rtcin(nv_off);
102		error = uiomove(&v, 1, uio);
103	}
104	return (error);
105
106}
107
108static int
109nvram_write(struct cdev *dev, struct uio *uio, int flags)
110{
111	int nv_off;
112	u_char v;
113	int error = 0;
114	int i;
115	uint16_t sum;
116
117	/* Assert that we understand the existing checksum first!  */
118	sum = rtcin(NVRAM_FIRST + CKSUM_MSB) << 8 |
119	      rtcin(NVRAM_FIRST + CKSUM_LSB);
120	for (i = CKSUM_FIRST; i <= CKSUM_LAST; i++)
121		sum -= rtcin(NVRAM_FIRST + i);
122	if (sum != 0)
123		return (EIO);
124	/* Bring in user data and write */
125	while (uio->uio_resid > 0 && error == 0) {
126		nv_off = uio->uio_offset + NVRAM_FIRST;
127		if (nv_off < NVRAM_FIRST || nv_off >= NVRAM_LAST)
128			return (0);	/* Signal EOF */
129		/* Single byte at a time */
130		error = uiomove(&v, 1, uio);
131		writertc(nv_off, v);
132	}
133	/* Recalculate checksum afterwards */
134	sum = 0;
135	for (i = CKSUM_FIRST; i <= CKSUM_LAST; i++)
136		sum += rtcin(NVRAM_FIRST + i);
137	writertc(NVRAM_FIRST + CKSUM_MSB, sum >> 8);
138	writertc(NVRAM_FIRST + CKSUM_LSB, sum);
139	return (error);
140}
141
142static int
143nvram_modevent(module_t mod __unused, int type, void *data __unused)
144{
145	switch (type) {
146	case MOD_LOAD:
147		nvram_dev = make_dev(&nvram_cdevsw, 0,
148		    UID_ROOT, GID_KMEM, 0640, "nvram");
149		break;
150	case MOD_UNLOAD:
151	case MOD_SHUTDOWN:
152		destroy_dev(nvram_dev);
153		break;
154	default:
155		return (EOPNOTSUPP);
156	}
157	return (0);
158}
159DEV_MODULE(nvram, nvram_modevent, NULL);
160