2 * Copyright (c) 2007 Peter Wemm
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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.
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
29 #include <sys/param.h>
30 #include <sys/systm.h>
31 #include <sys/kernel.h>
33 #include <sys/fcntl.h>
38 #include <sys/module.h>
43 * Linux-style /dev/nvram driver
45 * cmos ram starts at bytes 14 through 128, for a total of 114 bytes.
46 * The driver exposes byte 14 as file offset 0.
48 * Offsets 2 through 31 are checksummed at offset 32, 33.
49 * In order to avoid the possibility of making the machine unbootable at the
50 * bios level (press F1 to continue!), we refuse to allow writes if we do
51 * not see a pre-existing valid checksum. If the existing sum is invalid,
52 * then presumably we do not know how to make a sum that the bios will accept.
55 #define NVRAM_FIRST RTC_DIAG /* 14 */
56 #define NVRAM_LAST 128
63 static d_open_t nvram_open;
64 static d_read_t nvram_read;
65 static d_write_t nvram_write;
67 static struct cdev *nvram_dev;
68 static struct sx nvram_lock;
70 static struct cdevsw nvram_cdevsw = {
71 .d_version = D_VERSION,
74 .d_write = nvram_write,
79 nvram_open(struct cdev *dev __unused, int flags, int fmt __unused,
85 error = securelevel_gt(td->td_ucred, 0);
91 nvram_read(struct cdev *dev, struct uio *uio, int flags)
97 while (uio->uio_resid > 0 && error == 0) {
98 nv_off = uio->uio_offset + NVRAM_FIRST;
99 if (nv_off < NVRAM_FIRST || nv_off >= NVRAM_LAST)
100 return (0); /* Signal EOF */
101 /* Single byte at a time */
103 error = uiomove(&v, 1, uio);
110 nvram_write(struct cdev *dev, struct uio *uio, int flags)
118 sx_xlock(&nvram_lock);
120 /* Assert that we understand the existing checksum first! */
121 sum = rtcin(NVRAM_FIRST + CKSUM_MSB) << 8 |
122 rtcin(NVRAM_FIRST + CKSUM_LSB);
123 for (i = CKSUM_FIRST; i <= CKSUM_LAST; i++)
124 sum -= rtcin(NVRAM_FIRST + i);
126 sx_xunlock(&nvram_lock);
129 /* Bring in user data and write */
130 while (uio->uio_resid > 0 && error == 0) {
131 nv_off = uio->uio_offset + NVRAM_FIRST;
132 if (nv_off < NVRAM_FIRST || nv_off >= NVRAM_LAST) {
133 sx_xunlock(&nvram_lock);
134 return (0); /* Signal EOF */
136 /* Single byte at a time */
137 error = uiomove(&v, 1, uio);
140 /* Recalculate checksum afterwards */
142 for (i = CKSUM_FIRST; i <= CKSUM_LAST; i++)
143 sum += rtcin(NVRAM_FIRST + i);
144 writertc(NVRAM_FIRST + CKSUM_MSB, sum >> 8);
145 writertc(NVRAM_FIRST + CKSUM_LSB, sum);
146 sx_xunlock(&nvram_lock);
151 nvram_modevent(module_t mod __unused, int type, void *data __unused)
155 sx_init(&nvram_lock, "nvram");
156 nvram_dev = make_dev(&nvram_cdevsw, 0,
157 UID_ROOT, GID_KMEM, 0640, "nvram");
161 destroy_dev(nvram_dev);
162 sx_destroy(&nvram_lock);
169 DEV_MODULE(nvram, nvram_modevent, NULL);