1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2007 Peter Wemm 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 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. 15 * 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 26 * SUCH DAMAGE. 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 <isa/rtc.h> 41 42 /* 43 * Linux-style /dev/nvram driver 44 * 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. 47 * 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. 53 */ 54 55 #define NVRAM_FIRST RTC_DIAG /* 14 */ 56 #define NVRAM_LAST 128 57 58 #define CKSUM_FIRST 2 59 #define CKSUM_LAST 31 60 #define CKSUM_MSB 32 61 #define CKSUM_LSB 33 62 63 static d_open_t nvram_open; 64 static d_read_t nvram_read; 65 static d_write_t nvram_write; 66 67 static struct cdev *nvram_dev; 68 static struct sx nvram_lock; 69 70 static struct cdevsw nvram_cdevsw = { 71 .d_version = D_VERSION, 72 .d_open = nvram_open, 73 .d_read = nvram_read, 74 .d_write = nvram_write, 75 .d_name = "nvram", 76 }; 77 78 static int 79 nvram_open(struct cdev *dev __unused, int flags, int fmt __unused, 80 struct thread *td) 81 { 82 int error = 0; 83 84 if (flags & FWRITE) 85 error = securelevel_gt(td->td_ucred, 0); 86 87 return (error); 88 } 89 90 static int 91 nvram_read(struct cdev *dev, struct uio *uio, int flags) 92 { 93 int nv_off; 94 u_char v; 95 int error = 0; 96 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 */ 102 v = rtcin(nv_off); 103 error = uiomove(&v, 1, uio); 104 } 105 return (error); 106 107 } 108 109 static int 110 nvram_write(struct cdev *dev, struct uio *uio, int flags) 111 { 112 int nv_off; 113 u_char v; 114 int error = 0; 115 int i; 116 uint16_t sum; 117 118 sx_xlock(&nvram_lock); 119 120 /* 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); 125 if (sum != 0) { 126 sx_xunlock(&nvram_lock); 127 return (EIO); 128 } 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 */ 135 } 136 /* Single byte at a time */ 137 error = uiomove(&v, 1, uio); 138 writertc(nv_off, v); 139 } 140 /* Recalculate checksum afterwards */ 141 sum = 0; 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); 147 return (error); 148 } 149 150 static int 151 nvram_modevent(module_t mod __unused, int type, void *data __unused) 152 { 153 switch (type) { 154 case MOD_LOAD: 155 sx_init(&nvram_lock, "nvram"); 156 nvram_dev = make_dev(&nvram_cdevsw, 0, 157 UID_ROOT, GID_KMEM, 0640, "nvram"); 158 break; 159 case MOD_UNLOAD: 160 case MOD_SHUTDOWN: 161 destroy_dev(nvram_dev); 162 sx_destroy(&nvram_lock); 163 break; 164 default: 165 return (EOPNOTSUPP); 166 } 167 return (0); 168 } 169 DEV_MODULE(nvram, nvram_modevent, NULL); 170