drivers/base/power/trace.c

   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 #include <linux/pm-trace.h>
  11 #include <linux/export.h>
  12 #include <linux/rtc.h>
  13 #include <linux/suspend.h>
  14
  15 #include <linux/mc146818rtc.h>
  16
  17 #include "power.h"
  18
  19 /*
  20  * Horrid, horrid, horrid.
  21  *
  22  * It turns out that the _only_ piece of hardware that actually
  23  * keeps its value across a hard boot (and, more importantly, the
  24  * POST init sequence) is literally the realtime clock.
  25  *
  26  * Never mind that an RTC chip has 114 bytes (and often a whole
  27  * other bank of an additional 128 bytes) of nice SRAM that is
  28  * _designed_ to keep data - the POST will clear it. So we literally
  29  * can just use the few bytes of actual time data, which means that
  30  * we're really limited.
  31  *
  32  * It means, for example, that we can't use the seconds at all
  33  * (since the time between the hang and the boot might be more
  34  * than a minute), and we'd better not depend on the low bits of
  35  * the minutes either.
  36  *
  37  * There are the wday fields etc, but I wouldn't guarantee those
  38  * are dependable either. And if the date isn't valid, either the
  39  * hw or POST will do strange things.
  40  *
  41  * So we're left with:
  42  *  - year: 0-99
  43  *  - month: 0-11
  44  *  - day-of-month: 1-28
  45  *  - hour: 0-23
  46  *  - min: (0-30)*2
  47  *
  48  * Giving us a total range of 0-16128000 (0xf61800), ie less
  49  * than 24 bits of actual data we can save across reboots.
  50  *
  51  * And if your box can't boot in less than three minutes,
  52  * you're screwed.
  53  *
  54  * Now, almost 24 bits of data is pitifully small, so we need
  55  * to be pretty dense if we want to use it for anything nice.
  56  * What we do is that instead of saving off nice readable info,
  57  * we save off _hashes_ of information that we can hopefully
  58  * regenerate after the reboot.
  59  *
  60  * In particular, this means that we might be unlucky, and hit
  61  * a case where we have a hash collision, and we end up not
  62  * being able to tell for certain exactly which case happened.
  63  * But that's hopefully unlikely.
  64  *
  65  * What we do is to take the bits we can fit, and split them
  66  * into three parts (16*997*1009 = 16095568), and use the values
  67  * for:
  68  *  - 0-15: user-settable
  69  *  - 0-996: file + line number
  70  *  - 0-1008: device
  71  */
  72 #define USERHASH (16)
  73 #define FILEHASH (997)
  74 #define DEVHASH (1009)
  75
  76 #define DEVSEED (7919)
  77
  78 bool pm_trace_rtc_abused __read_mostly;
  79 EXPORT_SYMBOL_GPL(pm_trace_rtc_abused);
  80
  81 static unsigned int dev_hash_value;
  82
  83 static int set_magic_time(unsigned int user, unsigned int file, unsigned int device)
  84 {
  85         unsigned int n = user + USERHASH*(file + FILEHASH*device);
  86
  87         // June 7th, 2006
  88         static struct rtc_time time = {
  89                 .tm_sec = 0,
  90                 .tm_min = 0,
  91                 .tm_hour = 0,
  92                 .tm_mday = 7,
  93                 .tm_mon = 5,    // June - counting from zero
  94                 .tm_year = 106,
  95                 .tm_wday = 3,
  96                 .tm_yday = 160,
  97                 .tm_isdst = 1
  98         };
  99
 100         time.tm_year = (n % 100);
 101         n /= 100;
 102         time.tm_mon = (n % 12);
 103         n /= 12;
 104         time.tm_mday = (n % 28) + 1;
 105         n /= 28;
 106         time.tm_hour = (n % 24);
 107         n /= 24;
 108         time.tm_min = (n % 20) * 3;
 109         n /= 20;
 110         mc146818_set_time(&time);
 111         pm_trace_rtc_abused = true;
 112         return n ? -1 : 0;
 113 }
 114
 115 static unsigned int read_magic_time(void)
 116 {
 117         struct rtc_time time;
 118         unsigned int val;
 119
 120         mc146818_get_time(&time);
 121         pr_info("RTC time: %2d:%02d:%02d, date: %02d/%02d/%02d\n",
 122                 time.tm_hour, time.tm_min, time.tm_sec,
 123                 time.tm_mon + 1, time.tm_mday, time.tm_year % 100);
 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);