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
  14 #include <asm/rtc.h>
  15
  16 #include "power.h"
  17
  18 /*
  19  * Horrid, horrid, horrid.
  20  *
  21  * It turns out that the _only_ piece of hardware that actually
  22  * keeps its value across a hard boot (and, more importantly, the
  23  * POST init sequence) is literally the realtime clock.
  24  *
  25  * Never mind that an RTC chip has 114 bytes (and often a whole
  26  * other bank of an additional 128 bytes) of nice SRAM that is
  27  * _designed_ to keep data - the POST will clear it. So we literally
  28  * can just use the few bytes of actual time data, which means that
  29  * we're really limited.
  30  *
  31  * It means, for example, that we can't use the seconds at all
  32  * (since the time between the hang and the boot might be more
  33  * than a minute), and we'd better not depend on the low bits of
  34  * the minutes either.
  35  *
  36  * There are the wday fields etc, but I wouldn't guarantee those
  37  * are dependable either. And if the date isn't valid, either the
  38  * hw or POST will do strange things.
  39  *
  40  * So we're left with:
  41  *  - year: 0-99
  42  *  - month: 0-11
  43  *  - day-of-month: 1-28
  44  *  - hour: 0-23
  45  *  - min: (0-30)*2
  46  *
  47  * Giving us a total range of 0-16128000 (0xf61800), ie less
  48  * than 24 bits of actual data we can save across reboots.
  49  *
  50  * And if your box can't boot in less than three minutes,
  51  * you're screwed.
  52  *
  53  * Now, almost 24 bits of data is pitifully small, so we need
  54  * to be pretty dense if we want to use it for anything nice.
  55  * What we do is that instead of saving off nice readable info,
  56  * we save off _hashes_ of information that we can hopefully
  57  * regenerate after the reboot.
  58  *
  59  * In particular, this means that we might be unlucky, and hit
  60  * a case where we have a hash collision, and we end up not
  61  * being able to tell for certain exactly which case happened.
  62  * But that's hopefully unlikely.
  63  *
  64  * What we do is to take the bits we can fit, and split them
  65  * into three parts (16*997*1009 = 16095568), and use the values
  66  * for:
  67  *  - 0-15: user-settable
  68  *  - 0-996: file + line number
  69  *  - 0-1008: device
  70  */
  71 #define USERHASH (16)
  72 #define FILEHASH (997)
  73 #define DEVHASH (1009)
  74
  75 #define DEVSEED (7919)
  76
  77 static unsigned int dev_hash_value;
  78
  79 static int set_magic_time(unsigned int user, unsigned int file, unsigned int device)
  80 {
  81         unsigned int n = user + USERHASH*(file + FILEHASH*device);
  82
  83         // June 7th, 2006
  84         static struct rtc_time time = {
  85                 .tm_sec = 0,
  86                 .tm_min = 0,
  87                 .tm_hour = 0,
  88                 .tm_mday = 7,
  89                 .tm_mon = 5,    // June - counting from zero
  90                 .tm_year = 106,
  91                 .tm_wday = 3,
  92                 .tm_yday = 160,
  93                 .tm_isdst = 1
  94         };
  95
  96         time.tm_year = (n % 100);
  97         n /= 100;
  98         time.tm_mon = (n % 12);
  99         n /= 12;
 100         time.tm_mday = (n % 28) + 1;
 101         n /= 28;
 102         time.tm_hour = (n % 24);
 103         n /= 24;
 104         time.tm_min = (n % 20) * 3;
 105         n /= 20;
 106         set_rtc_time(&time);
 107         return n ? -1 : 0;
 108 }
 109
 110 static unsigned int read_magic_time(void)
 111 {
 112         struct rtc_time time;
 113         unsigned int val;
 114
 115         get_rtc_time(&time);
 116         pr_info("RTC time: %2d:%02d:%02d, date: %02d/%02d/%02d\n",
 117                 time.tm_hour, time.tm_min, time.tm_sec,
 118                 time.tm_mon + 1, time.tm_mday, time.tm_year % 100);
 119         val = time.tm_year;                             /* 100 years */
 120         if (val > 100)
 121                 val -= 100;
 122         val += time.tm_mon * 100;                       /* 12 months */
 123         val += (time.tm_mday-1) * 100 * 12;             /* 28 month-days */
 124         val += time.tm_hour * 100 * 12 * 28;            /* 24 hours */
 125         val += (time.tm_min / 3) * 100 * 12 * 28 * 24;  /* 20 3-minute intervals */
 126         return val;
 127 }
 128
 129 /*
 130  * This is just the sdbm hash function with a user-supplied
 131  * seed and final size parameter.
 132  */
 133 static unsigned int hash_string(unsigned int seed, const char *data, unsigned int mod)
 134 {
 135         unsigned char c;
 136         while ((c = *data++) != 0) {
 137                 seed = (seed << 16) + (seed << 6) - seed + c;
 138         }
 139         return seed % mod;
 140 }
 141
 142 void set_trace_device(struct device *dev)
 143 {
 144         dev_hash_value = hash_string(DEVSEED, dev_name(dev), DEVHASH);
 145 }
 146 EXPORT_SYMBOL(set_trace_device);
 147
 148 /*
 149  * We could just take the "tracedata" index into the .tracedata
 150  * section instead. Generating a hash of the data gives us a
 151  * chance to work across kernel versions, and perhaps more
 152  * importantly it also gives us valid/invalid check (ie we will
 153  * likely not give totally bogus reports - if the hash matches,
 154  * it's not any guarantee, but it's a high _likelihood_ that
 155  * the match is valid).
 156  */
 157 void generate_pm_trace(const void *tracedata, unsigned int user)
 158 {
 159         unsigned short lineno = *(unsigned short *)tracedata;
 160         const char *file = *(const char **)(tracedata + 2);
 161         unsigned int user_hash_value, file_hash_value;
 162
 163         user_hash_value = user % USERHASH;
 164         file_hash_value = hash_string(lineno, file, FILEHASH);
 165         set_magic_time(user_hash_value, file_hash_value, dev_hash_value);
 166 }
 167 EXPORT_SYMBOL(generate_pm_trace);
 168
 169 extern char __tracedata_start[], __tracedata_end[];
 170 static int show_file_hash(unsigned int value)
 171 {
 172         int match;
 173         char *tracedata;
 174
 175         match = 0;
 176         for (tracedata = __tracedata_start ; tracedata < __tracedata_end ;
 177                         tracedata += 2 + sizeof(unsigned long)) {
 178                 unsigned short lineno = *(unsigned short *)tracedata;
 179                 const char *file = *(const char **)(tracedata + 2);
 180                 unsigned int hash = hash_string(lineno, file, FILEHASH);
 181                 if (hash != value)
 182                         continue;
 183                 pr_info("  hash matches %s:%u\n", file, lineno);
 184                 match++;
 185         }
 186         return match;
 187 }
 188
 189 static int show_dev_hash(unsigned int value)
 190 {
 191         int match = 0;
 192         struct list_head *entry;
 193
 194         device_pm_lock();
 195         entry = dpm_list.prev;
 196         while (entry != &dpm_list) {
 197                 struct device * dev = to_device(entry);
 198                 unsigned int hash = hash_string(DEVSEED, dev_name(dev), DEVHASH);
 199                 if (hash == value) {
 200                         dev_info(dev, "hash matches\n");
 201                         match++;
 202                 }
 203                 entry = entry->prev;
 204         }
 205         device_pm_unlock();
 206         return match;
 207 }
 208
 209 static unsigned int hash_value_early_read;
 210
 211 int show_trace_dev_match(char *buf, size_t size)
 212 {
 213         unsigned int value = hash_value_early_read / (USERHASH * FILEHASH);
 214         int ret = 0;
 215         struct list_head *entry;
 216
 217         /*
 218          * It's possible that multiple devices will match the hash and we can't
 219          * tell which is the culprit, so it's best to output them all.
 220          */
 221         device_pm_lock();
 222         entry = dpm_list.prev;
 223         while (size && entry != &dpm_list) {
 224                 struct device *dev = to_device(entry);
 225                 unsigned int hash = hash_string(DEVSEED, dev_name(dev),
 226                                                 DEVHASH);
 227                 if (hash == value) {
 228                         int len = snprintf(buf, size, "%s\n",
 229                                             dev_driver_string(dev));
 230                         if (len > size)
 231                                 len = size;
 232                         buf += len;
 233                         ret += len;
 234                         size -= len;
 235                 }
 236                 entry = entry->prev;
 237         }
 238         device_pm_unlock();
 239         return ret;
 240 }
 241
 242 static int early_resume_init(void)
 243 {
 244         hash_value_early_read = read_magic_time();
 245         return 0;
 246 }
 247
 248 static int late_resume_init(void)
 249 {
 250         unsigned int val = hash_value_early_read;
 251         unsigned int user, file, dev;
 252
 253         user = val % USERHASH;
 254         val = val / USERHASH;
 255         file = val % FILEHASH;
 256         val = val / FILEHASH;
 257         dev = val /* % DEVHASH */;
 258
 259         pr_info("  Magic number: %d:%d:%d\n", user, file, dev);
 260         show_file_hash(file);
 261         show_dev_hash(dev);
 262         return 0;
 263 }
 264
 265 core_initcall(early_resume_init);
 266 late_initcall(late_resume_init);