xref: /openbmc/linux/drivers/base/power/trace.c (revision 49a76c08)
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 
set_magic_time(unsigned int user,unsigned int file,unsigned int device)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 
read_magic_time(void)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  */
hash_string(unsigned int seed,const char * data,unsigned int mod)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 
set_trace_device(struct device * dev)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  */
generate_pm_trace(const void * tracedata,unsigned int user)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[];
show_file_hash(unsigned int value)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 
show_dev_hash(unsigned int value)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 
show_trace_dev_match(char * buf,size_t size)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
pm_trace_notify(struct notifier_block * nb,unsigned long mode,void * _unused)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 
early_resume_init(void)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 
late_resume_init(void)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);
308