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
81bool pm_trace_rtc_abused __read_mostly;
82EXPORT_SYMBOL_GPL(pm_trace_rtc_abused);
83
84static unsigned int dev_hash_value;
85
86static 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: &time);
114 pm_trace_rtc_abused = true;
115 return n ? -1 : 0;
116}
117
118static unsigned int read_magic_time(void)
119{
120 struct rtc_time time;
121 unsigned int val;
122
123 if (mc146818_get_time(time: &time, timeout: 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 */
143static 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
152void set_trace_device(struct device *dev)
153{
154 dev_hash_value = hash_string(DEVSEED, data: dev_name(dev), DEVHASH);
155}
156EXPORT_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 */
167void 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(seed: lineno, data: file, FILEHASH);
178 set_magic_time(user: user_hash_value, file: file_hash_value, device: dev_hash_value);
179}
180EXPORT_SYMBOL(generate_pm_trace);
181
182extern char __tracedata_start[], __tracedata_end[];
183static 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(seed: lineno, data: 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
202static 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, data: 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
222static unsigned int hash_value_early_read;
223
224int 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, data: dev_name(dev),
239 DEVHASH);
240 if (hash == value) {
241 int len = snprintf(buf, size, fmt: "%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
255static int
256pm_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
272static struct notifier_block pm_trace_nb = {
273 .notifier_call = pm_trace_notify,
274};
275
276static 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(nb: &pm_trace_nb);
283 return 0;
284}
285
286static 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(value: file);
302 show_dev_hash(value: dev);
303 return 0;
304}
305
306core_initcall(early_resume_init);
307late_initcall(late_resume_init);
308