2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (c) 2007 Peter Wemm
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 #include <sys/param.h>
32 #include <sys/systm.h>
33 #include <sys/kernel.h>
35 #include <sys/fcntl.h>
40 #include <sys/module.h>
45 * Linux-style /dev/nvram driver
47 * cmos ram starts at bytes 14 through 128, for a total of 114 bytes.
48 * The driver exposes byte 14 as file offset 0.
50 * Offsets 2 through 31 are checksummed at offset 32, 33.
51 * In order to avoid the possibility of making the machine unbootable at the
52 * bios level (press F1 to continue!), we refuse to allow writes if we do
53 * not see a pre-existing valid checksum. If the existing sum is invalid,
54 * then presumably we do not know how to make a sum that the bios will accept.
57 #define NVRAM_FIRST RTC_DIAG /* 14 */
58 #define NVRAM_LAST 128
65 static d_open_t nvram_open;
66 static d_read_t nvram_read;
67 static d_write_t nvram_write;
69 static struct cdev *nvram_dev;
70 static struct sx nvram_lock;
72 static struct cdevsw nvram_cdevsw = {
73 .d_version = D_VERSION,
76 .d_write = nvram_write,
81 nvram_open(struct cdev *dev __unused, int flags, int fmt __unused,
87 error = securelevel_gt(td->td_ucred, 0);
93 nvram_read(struct cdev *dev, struct uio *uio, int flags)
99 while (uio->uio_resid > 0 && error == 0) {
100 nv_off = uio->uio_offset + NVRAM_FIRST;
101 if (nv_off < NVRAM_FIRST || nv_off >= NVRAM_LAST)
102 return (0); /* Signal EOF */
103 /* Single byte at a time */
105 error = uiomove(&v, 1, uio);
112 nvram_write(struct cdev *dev, struct uio *uio, int flags)
120 sx_xlock(&nvram_lock);
122 /* Assert that we understand the existing checksum first! */
123 sum = rtcin(NVRAM_FIRST + CKSUM_MSB) << 8 |
124 rtcin(NVRAM_FIRST + CKSUM_LSB);
125 for (i = CKSUM_FIRST; i <= CKSUM_LAST; i++)
126 sum -= rtcin(NVRAM_FIRST + i);
128 sx_xunlock(&nvram_lock);
131 /* Bring in user data and write */
132 while (uio->uio_resid > 0 && error == 0) {
133 nv_off = uio->uio_offset + NVRAM_FIRST;
134 if (nv_off < NVRAM_FIRST || nv_off >= NVRAM_LAST) {
135 sx_xunlock(&nvram_lock);
136 return (0); /* Signal EOF */
138 /* Single byte at a time */
139 error = uiomove(&v, 1, uio);
142 /* Recalculate checksum afterwards */
144 for (i = CKSUM_FIRST; i <= CKSUM_LAST; i++)
145 sum += rtcin(NVRAM_FIRST + i);
146 writertc(NVRAM_FIRST + CKSUM_MSB, sum >> 8);
147 writertc(NVRAM_FIRST + CKSUM_LSB, sum);
148 sx_xunlock(&nvram_lock);
153 nvram_modevent(module_t mod __unused, int type, void *data __unused)
157 sx_init(&nvram_lock, "nvram");
158 nvram_dev = make_dev(&nvram_cdevsw, 0,
159 UID_ROOT, GID_KMEM, 0640, "nvram");
163 destroy_dev(nvram_dev);
164 sx_destroy(&nvram_lock);
171 DEV_MODULE(nvram, nvram_modevent, NULL);