xref: /openbmc/linux/drivers/base/power/trace.c (revision e23feb16)
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 #include <linux/resume-trace.h>
11 #include <linux/export.h>
12 #include <linux/rtc.h>
13 
14 #include <asm/rtc.h>
15 
16 #include "power.h"
17 
18 /*
19  * Horrid, horrid, horrid.
20  *
21  * It turns out that the _only_ piece of hardware that actually
22  * keeps its value across a hard boot (and, more importantly, the
23  * POST init sequence) is literally the realtime clock.
24  *
25  * Never mind that an RTC chip has 114 bytes (and often a whole
26  * other bank of an additional 128 bytes) of nice SRAM that is
27  * _designed_ to keep data - the POST will clear it. So we literally
28  * can just use the few bytes of actual time data, which means that
29  * we're really limited.
30  *
31  * It means, for example, that we can't use the seconds at all
32  * (since the time between the hang and the boot might be more
33  * than a minute), and we'd better not depend on the low bits of
34  * the minutes either.
35  *
36  * There are the wday fields etc, but I wouldn't guarantee those
37  * are dependable either. And if the date isn't valid, either the
38  * hw or POST will do strange things.
39  *
40  * So we're left with:
41  *  - year: 0-99
42  *  - month: 0-11
43  *  - day-of-month: 1-28
44  *  - hour: 0-23
45  *  - min: (0-30)*2
46  *
47  * Giving us a total range of 0-16128000 (0xf61800), ie less
48  * than 24 bits of actual data we can save across reboots.
49  *
50  * And if your box can't boot in less than three minutes,
51  * you're screwed.
52  *
53  * Now, almost 24 bits of data is pitifully small, so we need
54  * to be pretty dense if we want to use it for anything nice.
55  * What we do is that instead of saving off nice readable info,
56  * we save off _hashes_ of information that we can hopefully
57  * regenerate after the reboot.
58  *
59  * In particular, this means that we might be unlucky, and hit
60  * a case where we have a hash collision, and we end up not
61  * being able to tell for certain exactly which case happened.
62  * But that's hopefully unlikely.
63  *
64  * What we do is to take the bits we can fit, and split them
65  * into three parts (16*997*1009 = 16095568), and use the values
66  * for:
67  *  - 0-15: user-settable
68  *  - 0-996: file + line number
69  *  - 0-1008: device
70  */
71 #define USERHASH (16)
72 #define FILEHASH (997)
73 #define DEVHASH (1009)
74 
75 #define DEVSEED (7919)
76 
77 static unsigned int dev_hash_value;
78 
79 static int set_magic_time(unsigned int user, unsigned int file, unsigned int device)
80 {
81 	unsigned int n = user + USERHASH*(file + FILEHASH*device);
82 
83 	// June 7th, 2006
84 	static struct rtc_time time = {
85 		.tm_sec = 0,
86 		.tm_min = 0,
87 		.tm_hour = 0,
88 		.tm_mday = 7,
89 		.tm_mon = 5,	// June - counting from zero
90 		.tm_year = 106,
91 		.tm_wday = 3,
92 		.tm_yday = 160,
93 		.tm_isdst = 1
94 	};
95 
96 	time.tm_year = (n % 100);
97 	n /= 100;
98 	time.tm_mon = (n % 12);
99 	n /= 12;
100 	time.tm_mday = (n % 28) + 1;
101 	n /= 28;
102 	time.tm_hour = (n % 24);
103 	n /= 24;
104 	time.tm_min = (n % 20) * 3;
105 	n /= 20;
106 	set_rtc_time(&time);
107 	return n ? -1 : 0;
108 }
109 
110 static unsigned int read_magic_time(void)
111 {
112 	struct rtc_time time;
113 	unsigned int val;
114 
115 	get_rtc_time(&time);
116 	pr_info("RTC time: %2d:%02d:%02d, date: %02d/%02d/%02d\n",
117 		time.tm_hour, time.tm_min, time.tm_sec,
118 		time.tm_mon + 1, time.tm_mday, time.tm_year % 100);
119 	val = time.tm_year;				/* 100 years */
120 	if (val > 100)
121 		val -= 100;
122 	val += time.tm_mon * 100;			/* 12 months */
123 	val += (time.tm_mday-1) * 100 * 12;		/* 28 month-days */
124 	val += time.tm_hour * 100 * 12 * 28;		/* 24 hours */
125 	val += (time.tm_min / 3) * 100 * 12 * 28 * 24;	/* 20 3-minute intervals */
126 	return val;
127 }
128 
129 /*
130  * This is just the sdbm hash function with a user-supplied
131  * seed and final size parameter.
132  */
133 static unsigned int hash_string(unsigned int seed, const char *data, unsigned int mod)
134 {
135 	unsigned char c;
136 	while ((c = *data++) != 0) {
137 		seed = (seed << 16) + (seed << 6) - seed + c;
138 	}
139 	return seed % mod;
140 }
141 
142 void set_trace_device(struct device *dev)
143 {
144 	dev_hash_value = hash_string(DEVSEED, dev_name(dev), DEVHASH);
145 }
146 EXPORT_SYMBOL(set_trace_device);
147 
148 /*
149  * We could just take the "tracedata" index into the .tracedata
150  * section instead. Generating a hash of the data gives us a
151  * chance to work across kernel versions, and perhaps more
152  * importantly it also gives us valid/invalid check (ie we will
153  * likely not give totally bogus reports - if the hash matches,
154  * it's not any guarantee, but it's a high _likelihood_ that
155  * the match is valid).
156  */
157 void generate_resume_trace(const void *tracedata, unsigned int user)
158 {
159 	unsigned short lineno = *(unsigned short *)tracedata;
160 	const char *file = *(const char **)(tracedata + 2);
161 	unsigned int user_hash_value, file_hash_value;
162 
163 	user_hash_value = user % USERHASH;
164 	file_hash_value = hash_string(lineno, file, FILEHASH);
165 	set_magic_time(user_hash_value, file_hash_value, dev_hash_value);
166 }
167 EXPORT_SYMBOL(generate_resume_trace);
168 
169 extern char __tracedata_start, __tracedata_end;
170 static int show_file_hash(unsigned int value)
171 {
172 	int match;
173 	char *tracedata;
174 
175 	match = 0;
176 	for (tracedata = &__tracedata_start ; tracedata < &__tracedata_end ;
177 			tracedata += 2 + sizeof(unsigned long)) {
178 		unsigned short lineno = *(unsigned short *)tracedata;
179 		const char *file = *(const char **)(tracedata + 2);
180 		unsigned int hash = hash_string(lineno, file, FILEHASH);
181 		if (hash != value)
182 			continue;
183 		pr_info("  hash matches %s:%u\n", file, lineno);
184 		match++;
185 	}
186 	return match;
187 }
188 
189 static int show_dev_hash(unsigned int value)
190 {
191 	int match = 0;
192 	struct list_head *entry;
193 
194 	device_pm_lock();
195 	entry = dpm_list.prev;
196 	while (entry != &dpm_list) {
197 		struct device * dev = to_device(entry);
198 		unsigned int hash = hash_string(DEVSEED, dev_name(dev), DEVHASH);
199 		if (hash == value) {
200 			dev_info(dev, "hash matches\n");
201 			match++;
202 		}
203 		entry = entry->prev;
204 	}
205 	device_pm_unlock();
206 	return match;
207 }
208 
209 static unsigned int hash_value_early_read;
210 
211 int show_trace_dev_match(char *buf, size_t size)
212 {
213 	unsigned int value = hash_value_early_read / (USERHASH * FILEHASH);
214 	int ret = 0;
215 	struct list_head *entry;
216 
217 	/*
218 	 * It's possible that multiple devices will match the hash and we can't
219 	 * tell which is the culprit, so it's best to output them all.
220 	 */
221 	device_pm_lock();
222 	entry = dpm_list.prev;
223 	while (size && entry != &dpm_list) {
224 		struct device *dev = to_device(entry);
225 		unsigned int hash = hash_string(DEVSEED, dev_name(dev),
226 						DEVHASH);
227 		if (hash == value) {
228 			int len = snprintf(buf, size, "%s\n",
229 					    dev_driver_string(dev));
230 			if (len > size)
231 				len = size;
232 			buf += len;
233 			ret += len;
234 			size -= len;
235 		}
236 		entry = entry->prev;
237 	}
238 	device_pm_unlock();
239 	return ret;
240 }
241 
242 static int early_resume_init(void)
243 {
244 	hash_value_early_read = read_magic_time();
245 	return 0;
246 }
247 
248 static int late_resume_init(void)
249 {
250 	unsigned int val = hash_value_early_read;
251 	unsigned int user, file, dev;
252 
253 	user = val % USERHASH;
254 	val = val / USERHASH;
255 	file = val % FILEHASH;
256 	val = val / FILEHASH;
257 	dev = val /* % DEVHASH */;
258 
259 	pr_info("  Magic number: %d:%d:%d\n", user, file, dev);
260 	show_file_hash(file);
261 	show_dev_hash(dev);
262 	return 0;
263 }
264 
265 core_initcall(early_resume_init);
266 late_initcall(late_resume_init);
267