FreeBSD/Linux Kernel Cross Reference
sys/dev/nvram/nvram.c
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 * $FreeBSD$
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/lock.h>
35 #include <sys/proc.h>
36 #include <sys/sx.h>
37 #include <sys/uio.h>
38 #include <sys/module.h>
39
40 #include <machine/clock.h>
41 #include <isa/rtc.h>
42
43 /*
44 * Linux-style /dev/nvram driver
45 *
46 * cmos ram starts at bytes 14 through 128, for a total of 114 bytes.
47 * The driver exposes byte 14 as file offset 0.
48 *
49 * Offsets 2 through 31 are checksummed at offset 32, 33.
50 * In order to avoid the possibility of making the machine unbootable at the
51 * bios level (press F1 to continue!), we refuse to allow writes if we do
52 * not see a pre-existing valid checksum. If the existing sum is invalid,
53 * then presumably we do not know how to make a sum that the bios will accept.
54 */
55
56 #define NVRAM_FIRST RTC_DIAG /* 14 */
57 #define NVRAM_LAST 128
58
59 #define CKSUM_FIRST 2
60 #define CKSUM_LAST 31
61 #define CKSUM_MSB 32
62 #define CKSUM_LSB 33
63
64 static d_open_t nvram_open;
65 static d_read_t nvram_read;
66 static d_write_t nvram_write;
67
68 static struct cdev *nvram_dev;
69 static struct sx nvram_lock;
70
71 static struct cdevsw nvram_cdevsw = {
72 .d_version = D_VERSION,
73 .d_open = nvram_open,
74 .d_read = nvram_read,
75 .d_write = nvram_write,
76 .d_name = "nvram",
77 };
78
79 static int
80 nvram_open(struct cdev *dev __unused, int flags, int fmt __unused,
81 struct thread *td)
82 {
83 int error = 0;
84
85 if (flags & FWRITE)
86 error = securelevel_gt(td->td_ucred, 0);
87
88 return (error);
89 }
90
91 static int
92 nvram_read(struct cdev *dev, struct uio *uio, int flags)
93 {
94 int nv_off;
95 u_char v;
96 int error = 0;
97
98 while (uio->uio_resid > 0 && error == 0) {
99 nv_off = uio->uio_offset + NVRAM_FIRST;
100 if (nv_off < NVRAM_FIRST || nv_off >= NVRAM_LAST)
101 return (0); /* Signal EOF */
102 /* Single byte at a time */
103 v = rtcin(nv_off);
104 error = uiomove(&v, 1, uio);
105 }
106 return (error);
107
108 }
109
110 static int
111 nvram_write(struct cdev *dev, struct uio *uio, int flags)
112 {
113 int nv_off;
114 u_char v;
115 int error = 0;
116 int i;
117 uint16_t sum;
118
119 sx_xlock(&nvram_lock);
120
121 /* Assert that we understand the existing checksum first! */
122 sum = rtcin(NVRAM_FIRST + CKSUM_MSB) << 8 |
123 rtcin(NVRAM_FIRST + CKSUM_LSB);
124 for (i = CKSUM_FIRST; i <= CKSUM_LAST; i++)
125 sum -= rtcin(NVRAM_FIRST + i);
126 if (sum != 0) {
127 sx_xunlock(&nvram_lock);
128 return (EIO);
129 }
130 /* Bring in user data and write */
131 while (uio->uio_resid > 0 && error == 0) {
132 nv_off = uio->uio_offset + NVRAM_FIRST;
133 if (nv_off < NVRAM_FIRST || nv_off >= NVRAM_LAST) {
134 sx_xunlock(&nvram_lock);
135 return (0); /* Signal EOF */
136 }
137 /* Single byte at a time */
138 error = uiomove(&v, 1, uio);
139 writertc(nv_off, v);
140 }
141 /* Recalculate checksum afterwards */
142 sum = 0;
143 for (i = CKSUM_FIRST; i <= CKSUM_LAST; i++)
144 sum += rtcin(NVRAM_FIRST + i);
145 writertc(NVRAM_FIRST + CKSUM_MSB, sum >> 8);
146 writertc(NVRAM_FIRST + CKSUM_LSB, sum);
147 sx_xunlock(&nvram_lock);
148 return (error);
149 }
150
151 static int
152 nvram_modevent(module_t mod __unused, int type, void *data __unused)
153 {
154 switch (type) {
155 case MOD_LOAD:
156 sx_init(&nvram_lock, "nvram");
157 nvram_dev = make_dev(&nvram_cdevsw, 0,
158 UID_ROOT, GID_KMEM, 0640, "nvram");
159 break;
160 case MOD_UNLOAD:
161 case MOD_SHUTDOWN:
162 destroy_dev(nvram_dev);
163 sx_destroy(&nvram_lock);
164 break;
165 default:
166 return (EOPNOTSUPP);
167 }
168 return (0);
169 }
170 DEV_MODULE(nvram, nvram_modevent, NULL);
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