drivers/base/power/trace.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * drivers/base/power/trace.c
   4  *
   5  * Copyright (C) 2006 Linus Torvalds
   6  *
   7  * Trace facility for suspend/resume problems, when none of the
   8  * devices may be working.
   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 #include <linux/init.h>
  17
  18 #include <linux/mc146818rtc.h>
  19
  20 #include "power.h"
  21
  22 /*
  23  * Horrid, horrid, horrid.
  24  *
  25  * It turns out that the _only_ piece of hardware that actually
  26  * keeps its value across a hard boot (and, more importantly, the
  27  * POST init sequence) is literally the realtime clock.
  28  *
  29  * Never mind that an RTC chip has 114 bytes (and often a whole
  30  * other bank of an additional 128 bytes) of nice SRAM that is
  31  * _designed_ to keep data - the POST will clear it. So we literally
  32  * can just use the few bytes of actual time data, which means that
  33  * we're really limited.
  34  *
  35  * It means, for example, that we can't use the seconds at all
  36  * (since the time between the hang and the boot might be more
  37  * than a minute), and we'd better not depend on the low bits of
  38  * the minutes either.
  39  *
  40  * There are the wday fields etc, but I wouldn't guarantee those
  41  * are dependable either. And if the date isn't valid, either the
  42  * hw or POST will do strange things.
  43  *
  44  * So we're left with:
  45  *  - year: 0-99
  46  *  - month: 0-11
  47  *  - day-of-month: 1-28
  48  *  - hour: 0-23
  49  *  - min: (0-30)*2
  50  *
  51  * Giving us a total range of 0-16128000 (0xf61800), ie less
  52  * than 24 bits of actual data we can save across reboots.
  53  *
  54  * And if your box can't boot in less than three minutes,
  55  * you're screwed.
  56  *
  57  * Now, almost 24 bits of data is pitifully small, so we need
  58  * to be pretty dense if we want to use it for anything nice.
  59  * What we do is that instead of saving off nice readable info,
  60  * we save off _hashes_ of information that we can hopefully
  61  * regenerate after the reboot.
  62  *
  63  * In particular, this means that we might be unlucky, and hit
  64  * a case where we have a hash collision, and we end up not
  65  * being able to tell for certain exactly which case happened.
  66  * But that's hopefully unlikely.
  67  *
  68  * What we do is to take the bits we can fit, and split them
  69  * into three parts (16*997*1009 = 16095568), and use the values
  70  * for:
  71  *  - 0-15: user-settable
  72  *  - 0-996: file + line number
  73  *  - 0-1008: device
  74  */
  75 #define USERHASH (16)
  76 #define FILEHASH (997)
  77 #define DEVHASH (1009)
  78
  79 #define DEVSEED (7919)
  80
  81 bool pm_trace_rtc_abused __read_mostly;
  82 EXPORT_SYMBOL_GPL(pm_trace_rtc_abused);
  83
  84 static unsigned int dev_hash_value;
  85
  86 static int set_magic_time(unsigned int user, unsigned int file, unsigned int device)
  87 {
  88         unsigned int n = user + USERHASH*(file + FILEHASH*device);
  89
  90         // June 7th, 2006
  91         static struct rtc_time time = {
  92                 .tm_sec = 0,
  93                 .tm_min = 0,
  94                 .tm_hour = 0,
  95                 .tm_mday = 7,
  96                 .tm_mon = 5,    // June - counting from zero
  97                 .tm_year = 106,
  98                 .tm_wday = 3,
  99                 .tm_yday = 160,
 100                 .tm_isdst = 1
 101         };
 102
 103         time.tm_year = (n % 100);
 104         n /= 100;
 105         time.tm_mon = (n % 12);
 106         n /= 12;
 107         time.tm_mday = (n % 28) + 1;
 108         n /= 28;
 109         time.tm_hour = (n % 24);
 110         n /= 24;
 111         time.tm_min = (n % 20) * 3;
 112         n /= 20;
 113         mc146818_set_time(&time);
 114         pm_trace_rtc_abused = true;
 115         return n ? -1 : 0;
 116 }
 117
 118 static unsigned int read_magic_time(void)
 119 {
 120         struct rtc_time time;
 121         unsigned int val;
 122
 123         if (mc146818_get_time(&time, 1000) < 0) {
 124                 pr_err("Unable to read current time from RTC\n");
 125                 return 0;
 126         }
 127
 128         pr_info("RTC time: %ptRt, date: %ptRd\n", &time, &time);
 129         val = time.tm_year;                             /* 100 years */
 130         if (val > 100)
 131                 val -= 100;
 132         val += time.tm_mon * 100;                       /* 12 months */
 133         val += (time.tm_mday-1) * 100 * 12;             /* 28 month-days */
 134         val += time.tm_hour * 100 * 12 * 28;            /* 24 hours */
 135         val += (time.tm_min / 3) * 100 * 12 * 28 * 24;  /* 20 3-minute intervals */
 136         return val;
 137 }
 138
 139 /*
 140  * This is just the sdbm hash function with a user-supplied
 141  * seed and final size parameter.
 142  */
 143 static unsigned int hash_string(unsigned int seed, const char *data, unsigned int mod)
 144 {
 145         unsigned char c;
 146         while ((c = *data++) != 0) {
 147                 seed = (seed << 16) + (seed << 6) - seed + c;
 148         }
 149         return seed % mod;
 150 }
 151
 152 void set_trace_device(struct device *dev)
 153 {
 154         dev_hash_value = hash_string(DEVSEED, dev_name(dev), DEVHASH);
 155 }
 156 EXPORT_SYMBOL(set_trace_device);
 157
 158 /*
 159  * We could just take the "tracedata" index into the .tracedata
 160  * section instead. Generating a hash of the data gives us a
 161  * chance to work across kernel versions, and perhaps more
 162  * importantly it also gives us valid/invalid check (ie we will
 163  * likely not give totally bogus reports - if the hash matches,
 164  * it's not any guarantee, but it's a high _likelihood_ that
 165  * the match is valid).
 166  */
 167 void generate_pm_trace(const void *tracedata, unsigned int user)
 168 {
 169         unsigned short lineno = *(unsigned short *)tracedata;
 170         const char *file = *(const char **)(tracedata + 2);
 171         unsigned int user_hash_value, file_hash_value;
 172
 173         if (!x86_platform.legacy.rtc)
 174                 return;
 175
 176         user_hash_value = user % USERHASH;
 177         file_hash_value = hash_string(lineno, file, FILEHASH);
 178         set_magic_time(user_hash_value, file_hash_value, dev_hash_value);
 179 }
 180 EXPORT_SYMBOL(generate_pm_trace);
 181
 182 extern char __tracedata_start[], __tracedata_end[];
 183 static int show_file_hash(unsigned int value)
 184 {
 185         int match;
 186         char *tracedata;
 187
 188         match = 0;
 189         for (tracedata = __tracedata_start ; tracedata < __tracedata_end ;
 190                         tracedata += 2 + sizeof(unsigned long)) {
 191                 unsigned short lineno = *(unsigned short *)tracedata;
 192                 const char *file = *(const char **)(tracedata + 2);
 193                 unsigned int hash = hash_string(lineno, file, FILEHASH);
 194                 if (hash != value)
 195                         continue;
 196                 pr_info("  hash matches %s:%u\n", file, lineno);
 197                 match++;
 198         }
 199         return match;
 200 }
 201
 202 static int show_dev_hash(unsigned int value)
 203 {
 204         int match = 0;
 205         struct list_head *entry;
 206
 207         device_pm_lock();
 208         entry = dpm_list.prev;
 209         while (entry != &dpm_list) {
 210                 struct device * dev = to_device(entry);
 211                 unsigned int hash = hash_string(DEVSEED, dev_name(dev), DEVHASH);
 212                 if (hash == value) {
 213                         dev_info(dev, "hash matches\n");
 214                         match++;
 215                 }
 216                 entry = entry->prev;
 217         }
 218         device_pm_unlock();
 219         return match;
 220 }
 221
 222 static unsigned int hash_value_early_read;
 223
 224 int show_trace_dev_match(char *buf, size_t size)
 225 {
 226         unsigned int value = hash_value_early_read / (USERHASH * FILEHASH);
 227         int ret = 0;
 228         struct list_head *entry;
 229
 230         /*
 231          * It's possible that multiple devices will match the hash and we can't
 232          * tell which is the culprit, so it's best to output them all.
 233          */
 234         device_pm_lock();
 235         entry = dpm_list.prev;
 236         while (size && entry != &dpm_list) {
 237                 struct device *dev = to_device(entry);
 238                 unsigned int hash = hash_string(DEVSEED, dev_name(dev),
 239                                                 DEVHASH);
 240                 if (hash == value) {
 241                         int len = snprintf(buf, size, "%s\n",
 242                                             dev_driver_string(dev));
 243                         if (len > size)
 244                                 len = size;
 245                         buf += len;
 246                         ret += len;
 247                         size -= len;
 248                 }
 249                 entry = entry->prev;
 250         }
 251         device_pm_unlock();
 252         return ret;
 253 }
 254
 255 static int
 256 pm_trace_notify(struct notifier_block *nb, unsigned long mode, void *_unused)
 257 {
 258         switch (mode) {
 259         case PM_POST_HIBERNATION:
 260         case PM_POST_SUSPEND:
 261                 if (pm_trace_rtc_abused) {
 262                         pm_trace_rtc_abused = false;
 263                         pr_warn("Possible incorrect RTC due to pm_trace, please use 'ntpdate' or 'rdate' to reset it.\n");
 264                 }
 265                 break;
 266         default:
 267                 break;
 268         }
 269         return 0;
 270 }
 271
 272 static struct notifier_block pm_trace_nb = {
 273         .notifier_call = pm_trace_notify,
 274 };
 275
 276 static int __init early_resume_init(void)
 277 {
 278         if (!x86_platform.legacy.rtc)
 279                 return 0;
 280
 281         hash_value_early_read = read_magic_time();
 282         register_pm_notifier(&pm_trace_nb);
 283         return 0;
 284 }
 285
 286 static int __init late_resume_init(void)
 287 {
 288         unsigned int val = hash_value_early_read;
 289         unsigned int user, file, dev;
 290
 291         if (!x86_platform.legacy.rtc)
 292                 return 0;
 293
 294         user = val % USERHASH;
 295         val = val / USERHASH;
 296         file = val % FILEHASH;
 297         val = val / FILEHASH;
 298         dev = val /* % DEVHASH */;
 299
 300         pr_info("  Magic number: %d:%d:%d\n", user, file, dev);
 301         show_file_hash(file);
 302         show_dev_hash(dev);
 303         return 0;
 304 }
 305
 306 core_initcall(early_resume_init);
 307 late_initcall(late_resume_init);