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