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/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
  77static unsigned int dev_hash_value;
  78
  79static 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
 110static 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 */
 133static 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
 142void set_trace_device(struct device *dev)
 143{
 144        dev_hash_value = hash_string(DEVSEED, dev_name(dev), DEVHASH);
 145}
 146EXPORT_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 */
 157void generate_resume_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}
 167EXPORT_SYMBOL(generate_resume_trace);
 168
 169extern char __tracedata_start, __tracedata_end;
 170static 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
 189static 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
 209static unsigned int hash_value_early_read;
 210
 211int 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
 242static int early_resume_init(void)
 243{
 244        hash_value_early_read = read_magic_time();
 245        return 0;
 246}
 247
 248static 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
 265core_initcall(early_resume_init);
 266late_initcall(late_resume_init);
 267