2 * drivers/base/power/trace.c
4 * Copyright (C) 2006 Linus Torvalds
6 * Trace facility for suspend/resume problems, when none of the
7 * devices may be working.
10 #include <linux/pm-trace.h>
11 #include <linux/export.h>
12 #include <linux/rtc.h>
13 #include <linux/suspend.h>
15 #include <linux/mc146818rtc.h>
20 * Horrid, horrid, horrid.
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.
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.
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
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.
44 * - day-of-month: 1-28
48 * Giving us a total range of 0-16128000 (0xf61800), ie less
49 * than 24 bits of actual data we can save across reboots.
51 * And if your box can't boot in less than three minutes,
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.
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.
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
68 * - 0-15: user-settable
69 * - 0-996: file + line number
73 #define FILEHASH (997)
74 #define DEVHASH (1009)
76 #define DEVSEED (7919)
78 bool pm_trace_rtc_abused __read_mostly;
79 EXPORT_SYMBOL_GPL(pm_trace_rtc_abused);
81 static unsigned int dev_hash_value;
83 static int set_magic_time(unsigned int user, unsigned int file, unsigned int device)
85 unsigned int n = user + USERHASH*(file + FILEHASH*device);
88 static struct rtc_time time = {
93 .tm_mon = 5, // June - counting from zero
100 time.tm_year = (n % 100);
102 time.tm_mon = (n % 12);
104 time.tm_mday = (n % 28) + 1;
106 time.tm_hour = (n % 24);
108 time.tm_min = (n % 20) * 3;
110 mc146818_set_time(&time);
111 pm_trace_rtc_abused = true;
115 static unsigned int read_magic_time(void)
117 struct rtc_time time;
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 */
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 */
135 * This is just the sdbm hash function with a user-supplied
136 * seed and final size parameter.
138 static unsigned int hash_string(unsigned int seed, const char *data, unsigned int mod)
141 while ((c = *data++) != 0) {
142 seed = (seed << 16) + (seed << 6) - seed + c;
147 void set_trace_device(struct device *dev)
149 dev_hash_value = hash_string(DEVSEED, dev_name(dev), DEVHASH);
151 EXPORT_SYMBOL(set_trace_device);
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).
162 void generate_pm_trace(const void *tracedata, unsigned int user)
164 unsigned short lineno = *(unsigned short *)tracedata;
165 const char *file = *(const char **)(tracedata + 2);
166 unsigned int user_hash_value, file_hash_value;
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);
172 EXPORT_SYMBOL(generate_pm_trace);
174 extern char __tracedata_start[], __tracedata_end[];
175 static int show_file_hash(unsigned int value)
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);
188 pr_info(" hash matches %s:%u\n", file, lineno);
194 static int show_dev_hash(unsigned int value)
197 struct list_head *entry;
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);
205 dev_info(dev, "hash matches\n");
214 static unsigned int hash_value_early_read;
216 int show_trace_dev_match(char *buf, size_t size)
218 unsigned int value = hash_value_early_read / (USERHASH * FILEHASH);
220 struct list_head *entry;
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.
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),
233 int len = snprintf(buf, size, "%s\n",
234 dev_driver_string(dev));
248 pm_trace_notify(struct notifier_block *nb, unsigned long mode, void *_unused)
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");
264 static struct notifier_block pm_trace_nb = {
265 .notifier_call = pm_trace_notify,
268 static int early_resume_init(void)
270 hash_value_early_read = read_magic_time();
271 register_pm_notifier(&pm_trace_nb);
275 static int late_resume_init(void)
277 unsigned int val = hash_value_early_read;
278 unsigned int user, file, dev;
280 user = val % USERHASH;
281 val = val / USERHASH;
282 file = val % FILEHASH;
283 val = val / FILEHASH;
284 dev = val /* % DEVHASH */;
286 pr_info(" Magic number: %d:%d:%d\n", user, file, dev);
287 show_file_hash(file);
292 core_initcall(early_resume_init);
293 late_initcall(late_resume_init);