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