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