1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * drivers/base/power/trace.c 4 * 5 * Copyright (C) 2006 Linus Torvalds 6 * 7 * Trace facility for suspend/resume problems, when none of the 8 * devices may be working. 9 */ 10 #define pr_fmt(fmt) "PM: " fmt 11 12 #include <linux/pm-trace.h> 13 #include <linux/export.h> 14 #include <linux/rtc.h> 15 #include <linux/suspend.h> 16 #include <linux/init.h> 17 18 #include <linux/mc146818rtc.h> 19 20 #include "power.h" 21 22 /* 23 * Horrid, horrid, horrid. 24 * 25 * It turns out that the _only_ piece of hardware that actually 26 * keeps its value across a hard boot (and, more importantly, the 27 * POST init sequence) is literally the realtime clock. 28 * 29 * Never mind that an RTC chip has 114 bytes (and often a whole 30 * other bank of an additional 128 bytes) of nice SRAM that is 31 * _designed_ to keep data - the POST will clear it. So we literally 32 * can just use the few bytes of actual time data, which means that 33 * we're really limited. 34 * 35 * It means, for example, that we can't use the seconds at all 36 * (since the time between the hang and the boot might be more 37 * than a minute), and we'd better not depend on the low bits of 38 * the minutes either. 39 * 40 * There are the wday fields etc, but I wouldn't guarantee those 41 * are dependable either. And if the date isn't valid, either the 42 * hw or POST will do strange things. 43 * 44 * So we're left with: 45 * - year: 0-99 46 * - month: 0-11 47 * - day-of-month: 1-28 48 * - hour: 0-23 49 * - min: (0-30)*2 50 * 51 * Giving us a total range of 0-16128000 (0xf61800), ie less 52 * than 24 bits of actual data we can save across reboots. 53 * 54 * And if your box can't boot in less than three minutes, 55 * you're screwed. 56 * 57 * Now, almost 24 bits of data is pitifully small, so we need 58 * to be pretty dense if we want to use it for anything nice. 59 * What we do is that instead of saving off nice readable info, 60 * we save off _hashes_ of information that we can hopefully 61 * regenerate after the reboot. 62 * 63 * In particular, this means that we might be unlucky, and hit 64 * a case where we have a hash collision, and we end up not 65 * being able to tell for certain exactly which case happened. 66 * But that's hopefully unlikely. 67 * 68 * What we do is to take the bits we can fit, and split them 69 * into three parts (16*997*1009 = 16095568), and use the values 70 * for: 71 * - 0-15: user-settable 72 * - 0-996: file + line number 73 * - 0-1008: device 74 */ 75 #define USERHASH (16) 76 #define FILEHASH (997) 77 #define DEVHASH (1009) 78 79 #define DEVSEED (7919) 80 81 bool pm_trace_rtc_abused __read_mostly; 82 EXPORT_SYMBOL_GPL(pm_trace_rtc_abused); 83 84 static unsigned int dev_hash_value; 85 86 static int set_magic_time(unsigned int user, unsigned int file, unsigned int device) 87 { 88 unsigned int n = user + USERHASH*(file + FILEHASH*device); 89 90 // June 7th, 2006 91 static struct rtc_time time = { 92 .tm_sec = 0, 93 .tm_min = 0, 94 .tm_hour = 0, 95 .tm_mday = 7, 96 .tm_mon = 5, // June - counting from zero 97 .tm_year = 106, 98 .tm_wday = 3, 99 .tm_yday = 160, 100 .tm_isdst = 1 101 }; 102 103 time.tm_year = (n % 100); 104 n /= 100; 105 time.tm_mon = (n % 12); 106 n /= 12; 107 time.tm_mday = (n % 28) + 1; 108 n /= 28; 109 time.tm_hour = (n % 24); 110 n /= 24; 111 time.tm_min = (n % 20) * 3; 112 n /= 20; 113 mc146818_set_time(&time); 114 pm_trace_rtc_abused = true; 115 return n ? -1 : 0; 116 } 117 118 static unsigned int read_magic_time(void) 119 { 120 struct rtc_time time; 121 unsigned int val; 122 123 mc146818_get_time(&time); 124 pr_info("RTC time: %ptRt, date: %ptRd\n", &time, &time); 125 val = time.tm_year; /* 100 years */ 126 if (val > 100) 127 val -= 100; 128 val += time.tm_mon * 100; /* 12 months */ 129 val += (time.tm_mday-1) * 100 * 12; /* 28 month-days */ 130 val += time.tm_hour * 100 * 12 * 28; /* 24 hours */ 131 val += (time.tm_min / 3) * 100 * 12 * 28 * 24; /* 20 3-minute intervals */ 132 return val; 133 } 134 135 /* 136 * This is just the sdbm hash function with a user-supplied 137 * seed and final size parameter. 138 */ 139 static unsigned int hash_string(unsigned int seed, const char *data, unsigned int mod) 140 { 141 unsigned char c; 142 while ((c = *data++) != 0) { 143 seed = (seed << 16) + (seed << 6) - seed + c; 144 } 145 return seed % mod; 146 } 147 148 void set_trace_device(struct device *dev) 149 { 150 dev_hash_value = hash_string(DEVSEED, dev_name(dev), DEVHASH); 151 } 152 EXPORT_SYMBOL(set_trace_device); 153 154 /* 155 * We could just take the "tracedata" index into the .tracedata 156 * section instead. Generating a hash of the data gives us a 157 * chance to work across kernel versions, and perhaps more 158 * importantly it also gives us valid/invalid check (ie we will 159 * likely not give totally bogus reports - if the hash matches, 160 * it's not any guarantee, but it's a high _likelihood_ that 161 * the match is valid). 162 */ 163 void generate_pm_trace(const void *tracedata, unsigned int user) 164 { 165 unsigned short lineno = *(unsigned short *)tracedata; 166 const char *file = *(const char **)(tracedata + 2); 167 unsigned int user_hash_value, file_hash_value; 168 169 if (!x86_platform.legacy.rtc) 170 return; 171 172 user_hash_value = user % USERHASH; 173 file_hash_value = hash_string(lineno, file, FILEHASH); 174 set_magic_time(user_hash_value, file_hash_value, dev_hash_value); 175 } 176 EXPORT_SYMBOL(generate_pm_trace); 177 178 extern char __tracedata_start[], __tracedata_end[]; 179 static int show_file_hash(unsigned int value) 180 { 181 int match; 182 char *tracedata; 183 184 match = 0; 185 for (tracedata = __tracedata_start ; tracedata < __tracedata_end ; 186 tracedata += 2 + sizeof(unsigned long)) { 187 unsigned short lineno = *(unsigned short *)tracedata; 188 const char *file = *(const char **)(tracedata + 2); 189 unsigned int hash = hash_string(lineno, file, FILEHASH); 190 if (hash != value) 191 continue; 192 pr_info(" hash matches %s:%u\n", file, lineno); 193 match++; 194 } 195 return match; 196 } 197 198 static int show_dev_hash(unsigned int value) 199 { 200 int match = 0; 201 struct list_head *entry; 202 203 device_pm_lock(); 204 entry = dpm_list.prev; 205 while (entry != &dpm_list) { 206 struct device * dev = to_device(entry); 207 unsigned int hash = hash_string(DEVSEED, dev_name(dev), DEVHASH); 208 if (hash == value) { 209 dev_info(dev, "hash matches\n"); 210 match++; 211 } 212 entry = entry->prev; 213 } 214 device_pm_unlock(); 215 return match; 216 } 217 218 static unsigned int hash_value_early_read; 219 220 int show_trace_dev_match(char *buf, size_t size) 221 { 222 unsigned int value = hash_value_early_read / (USERHASH * FILEHASH); 223 int ret = 0; 224 struct list_head *entry; 225 226 /* 227 * It's possible that multiple devices will match the hash and we can't 228 * tell which is the culprit, so it's best to output them all. 229 */ 230 device_pm_lock(); 231 entry = dpm_list.prev; 232 while (size && entry != &dpm_list) { 233 struct device *dev = to_device(entry); 234 unsigned int hash = hash_string(DEVSEED, dev_name(dev), 235 DEVHASH); 236 if (hash == value) { 237 int len = snprintf(buf, size, "%s\n", 238 dev_driver_string(dev)); 239 if (len > size) 240 len = size; 241 buf += len; 242 ret += len; 243 size -= len; 244 } 245 entry = entry->prev; 246 } 247 device_pm_unlock(); 248 return ret; 249 } 250 251 static int 252 pm_trace_notify(struct notifier_block *nb, unsigned long mode, void *_unused) 253 { 254 switch (mode) { 255 case PM_POST_HIBERNATION: 256 case PM_POST_SUSPEND: 257 if (pm_trace_rtc_abused) { 258 pm_trace_rtc_abused = false; 259 pr_warn("Possible incorrect RTC due to pm_trace, please use 'ntpdate' or 'rdate' to reset it.\n"); 260 } 261 break; 262 default: 263 break; 264 } 265 return 0; 266 } 267 268 static struct notifier_block pm_trace_nb = { 269 .notifier_call = pm_trace_notify, 270 }; 271 272 static int __init early_resume_init(void) 273 { 274 if (!x86_platform.legacy.rtc) 275 return 0; 276 277 hash_value_early_read = read_magic_time(); 278 register_pm_notifier(&pm_trace_nb); 279 return 0; 280 } 281 282 static int __init late_resume_init(void) 283 { 284 unsigned int val = hash_value_early_read; 285 unsigned int user, file, dev; 286 287 if (!x86_platform.legacy.rtc) 288 return 0; 289 290 user = val % USERHASH; 291 val = val / USERHASH; 292 file = val % FILEHASH; 293 val = val / FILEHASH; 294 dev = val /* % DEVHASH */; 295 296 pr_info(" Magic number: %d:%d:%d\n", user, file, dev); 297 show_file_hash(file); 298 show_dev_hash(dev); 299 return 0; 300 } 301 302 core_initcall(early_resume_init); 303 late_initcall(late_resume_init); 304