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);
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, 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, 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(lineno, file, FILEHASH);
178	set_magic_time(user_hash_value, file_hash_value, 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(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
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, 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, 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
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(&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(file);
302	show_dev_hash(dev);
303	return 0;
304}
305
306core_initcall(early_resume_init);
307late_initcall(late_resume_init);
308