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#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
17#include <linux/mc146818rtc.h>
18
19#include "power.h"
20
21/*
22 * Horrid, horrid, horrid.
23 *
24 * It turns out that the _only_ piece of hardware that actually
25 * keeps its value across a hard boot (and, more importantly, the
26 * POST init sequence) is literally the realtime clock.
27 *
28 * Never mind that an RTC chip has 114 bytes (and often a whole
29 * other bank of an additional 128 bytes) of nice SRAM that is
30 * _designed_ to keep data - the POST will clear it. So we literally
31 * can just use the few bytes of actual time data, which means that
32 * we're really limited.
33 *
34 * It means, for example, that we can't use the seconds at all
35 * (since the time between the hang and the boot might be more
36 * than a minute), and we'd better not depend on the low bits of
37 * the minutes either.
38 *
39 * There are the wday fields etc, but I wouldn't guarantee those
40 * are dependable either. And if the date isn't valid, either the
41 * hw or POST will do strange things.
42 *
43 * So we're left with:
44 * - year: 0-99
45 * - month: 0-11
46 * - day-of-month: 1-28
47 * - hour: 0-23
48 * - min: (0-30)*2
49 *
50 * Giving us a total range of 0-16128000 (0xf61800), ie less
51 * than 24 bits of actual data we can save across reboots.
52 *
53 * And if your box can't boot in less than three minutes,
54 * you're screwed.
55 *
56 * Now, almost 24 bits of data is pitifully small, so we need
57 * to be pretty dense if we want to use it for anything nice.
58 * What we do is that instead of saving off nice readable info,
59 * we save off _hashes_ of information that we can hopefully
60 * regenerate after the reboot.
61 *
62 * In particular, this means that we might be unlucky, and hit
63 * a case where we have a hash collision, and we end up not
64 * being able to tell for certain exactly which case happened.
65 * But that's hopefully unlikely.
66 *
67 * What we do is to take the bits we can fit, and split them
68 * into three parts (16*997*1009 = 16095568), and use the values
69 * for:
70 * - 0-15: user-settable
71 * - 0-996: file + line number
72 * - 0-1008: device
73 */
74#define USERHASH (16)
75#define FILEHASH (997)
76#define DEVHASH (1009)
77
78#define DEVSEED (7919)
79
80bool pm_trace_rtc_abused __read_mostly;
81EXPORT_SYMBOL_GPL(pm_trace_rtc_abused);
82
83static unsigned int dev_hash_value;
84
85static int set_magic_time(unsigned int user, unsigned int file, unsigned int device)
86{
87 unsigned int n = user + USERHASH*(file + FILEHASH*device);
88
89 // June 7th, 2006
90 static struct rtc_time time = {
91 .tm_sec = 0,
92 .tm_min = 0,
93 .tm_hour = 0,
94 .tm_mday = 7,
95 .tm_mon = 5, // June - counting from zero
96 .tm_year = 106,
97 .tm_wday = 3,
98 .tm_yday = 160,
99 .tm_isdst = 1
100 };
101
102 time.tm_year = (n % 100);
103 n /= 100;
104 time.tm_mon = (n % 12);
105 n /= 12;
106 time.tm_mday = (n % 28) + 1;
107 n /= 28;
108 time.tm_hour = (n % 24);
109 n /= 24;
110 time.tm_min = (n % 20) * 3;
111 n /= 20;
112 mc146818_set_time(&time);
113 pm_trace_rtc_abused = true;
114 return n ? -1 : 0;
115}
116
117static unsigned int read_magic_time(void)
118{
119 struct rtc_time time;
120 unsigned int val;
121
122 mc146818_get_time(&time);
123 pr_info("RTC time: %ptRt, date: %ptRd\n", &time, &time);
124 val = time.tm_year; /* 100 years */
125 if (val > 100)
126 val -= 100;
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 */
131 return val;
132}
133
134/*
135 * This is just the sdbm hash function with a user-supplied
136 * seed and final size parameter.
137 */
138static unsigned int hash_string(unsigned int seed, const char *data, unsigned int mod)
139{
140 unsigned char c;
141 while ((c = *data++) != 0) {
142 seed = (seed << 16) + (seed << 6) - seed + c;
143 }
144 return seed % mod;
145}
146
147void set_trace_device(struct device *dev)
148{
149 dev_hash_value = hash_string(DEVSEED, dev_name(dev), DEVHASH);
150}
151EXPORT_SYMBOL(set_trace_device);
152
153/*
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).
161 */
162void generate_pm_trace(const void *tracedata, unsigned int user)
163{
164 unsigned short lineno = *(unsigned short *)tracedata;
165 const char *file = *(const char **)(tracedata + 2);
166 unsigned int user_hash_value, file_hash_value;
167
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);
171}
172EXPORT_SYMBOL(generate_pm_trace);
173
174extern char __tracedata_start[], __tracedata_end[];
175static int show_file_hash(unsigned int value)
176{
177 int match;
178 char *tracedata;
179
180 match = 0;
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);
186 if (hash != value)
187 continue;
188 pr_info(" hash matches %s:%u\n", file, lineno);
189 match++;
190 }
191 return match;
192}
193
194static int show_dev_hash(unsigned int value)
195{
196 int match = 0;
197 struct list_head *entry;
198
199 device_pm_lock();
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);
204 if (hash == value) {
205 dev_info(dev, "hash matches\n");
206 match++;
207 }
208 entry = entry->prev;
209 }
210 device_pm_unlock();
211 return match;
212}
213
214static unsigned int hash_value_early_read;
215
216int show_trace_dev_match(char *buf, size_t size)
217{
218 unsigned int value = hash_value_early_read / (USERHASH * FILEHASH);
219 int ret = 0;
220 struct list_head *entry;
221
222 /*
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.
225 */
226 device_pm_lock();
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),
231 DEVHASH);
232 if (hash == value) {
233 int len = snprintf(buf, size, "%s\n",
234 dev_driver_string(dev));
235 if (len > size)
236 len = size;
237 buf += len;
238 ret += len;
239 size -= len;
240 }
241 entry = entry->prev;
242 }
243 device_pm_unlock();
244 return ret;
245}
246
247static int
248pm_trace_notify(struct notifier_block *nb, unsigned long mode, void *_unused)
249{
250 switch (mode) {
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");
256 }
257 break;
258 default:
259 break;
260 }
261 return 0;
262}
263
264static struct notifier_block pm_trace_nb = {
265 .notifier_call = pm_trace_notify,
266};
267
268static int early_resume_init(void)
269{
270 hash_value_early_read = read_magic_time();
271 register_pm_notifier(&pm_trace_nb);
272 return 0;
273}
274
275static int late_resume_init(void)
276{
277 unsigned int val = hash_value_early_read;
278 unsigned int user, file, dev;
279
280 user = val % USERHASH;
281 val = val / USERHASH;
282 file = val % FILEHASH;
283 val = val / FILEHASH;
284 dev = val /* % DEVHASH */;
285
286 pr_info(" Magic number: %d:%d:%d\n", user, file, dev);
287 show_file_hash(file);
288 show_dev_hash(dev);
289 return 0;
290}
291
292core_initcall(early_resume_init);
293late_initcall(late_resume_init);
294