2 * drivers/base/power/trace.c
4 * Copyright (C) 2006 Linus Torvalds
6 * Trace facility for suspend/resume problems, when none of the
7 * devices may be working.
10 #include <linux/pm-trace.h>
11 #include <linux/export.h>
12 #include <linux/rtc.h>
13 #include <linux/suspend.h>
15 #include <linux/mc146818rtc.h>
20 * Horrid, horrid, horrid.
22 * It turns out that the _only_ piece of hardware that actually
23 * keeps its value across a hard boot (and, more importantly, the
24 * POST init sequence) is literally the realtime clock.
26 * Never mind that an RTC chip has 114 bytes (and often a whole
27 * other bank of an additional 128 bytes) of nice SRAM that is
28 * _designed_ to keep data - the POST will clear it. So we literally
29 * can just use the few bytes of actual time data, which means that
30 * we're really limited.
32 * It means, for example, that we can't use the seconds at all
33 * (since the time between the hang and the boot might be more
34 * than a minute), and we'd better not depend on the low bits of
37 * There are the wday fields etc, but I wouldn't guarantee those
38 * are dependable either. And if the date isn't valid, either the
39 * hw or POST will do strange things.
44 * - day-of-month: 1-28
48 * Giving us a total range of 0-16128000 (0xf61800), ie less
49 * than 24 bits of actual data we can save across reboots.
51 * And if your box can't boot in less than three minutes,
54 * Now, almost 24 bits of data is pitifully small, so we need
55 * to be pretty dense if we want to use it for anything nice.
56 * What we do is that instead of saving off nice readable info,
57 * we save off _hashes_ of information that we can hopefully
58 * regenerate after the reboot.
60 * In particular, this means that we might be unlucky, and hit
61 * a case where we have a hash collision, and we end up not
62 * being able to tell for certain exactly which case happened.
63 * But that's hopefully unlikely.
65 * What we do is to take the bits we can fit, and split them
66 * into three parts (16*997*1009 = 16095568), and use the values
68 * - 0-15: user-settable
69 * - 0-996: file + line number
73 #define FILEHASH (997)
74 #define DEVHASH (1009)
76 #define DEVSEED (7919)
78 bool pm_trace_rtc_abused __read_mostly
;
79 EXPORT_SYMBOL_GPL(pm_trace_rtc_abused
);
81 static unsigned int dev_hash_value
;
83 static int set_magic_time(unsigned int user
, unsigned int file
, unsigned int device
)
85 unsigned int n
= user
+ USERHASH
*(file
+ FILEHASH
*device
);
88 static struct rtc_time time
= {
93 .tm_mon
= 5, // June - counting from zero
100 time
.tm_year
= (n
% 100);
102 time
.tm_mon
= (n
% 12);
104 time
.tm_mday
= (n
% 28) + 1;
106 time
.tm_hour
= (n
% 24);
108 time
.tm_min
= (n
% 20) * 3;
110 mc146818_set_time(&time
);
111 pm_trace_rtc_abused
= true;
115 static unsigned int read_magic_time(void)
117 struct rtc_time time
;
120 mc146818_get_time(&time
);
121 pr_info("RTC time: %2d:%02d:%02d, date: %02d/%02d/%02d\n",
122 time
.tm_hour
, time
.tm_min
, time
.tm_sec
,
123 time
.tm_mon
+ 1, time
.tm_mday
, time
.tm_year
% 100);
124 val
= time
.tm_year
; /* 100 years */
127 val
+= time
.tm_mon
* 100; /* 12 months */
128 val
+= (time
.tm_mday
-1) * 100 * 12; /* 28 month-days */
129 val
+= time
.tm_hour
* 100 * 12 * 28; /* 24 hours */
130 val
+= (time
.tm_min
/ 3) * 100 * 12 * 28 * 24; /* 20 3-minute intervals */
135 * This is just the sdbm hash function with a user-supplied
136 * seed and final size parameter.
138 static unsigned int hash_string(unsigned int seed
, const char *data
, unsigned int mod
)
141 while ((c
= *data
++) != 0) {
142 seed
= (seed
<< 16) + (seed
<< 6) - seed
+ c
;
147 void set_trace_device(struct device
*dev
)
149 dev_hash_value
= hash_string(DEVSEED
, dev_name(dev
), DEVHASH
);
151 EXPORT_SYMBOL(set_trace_device
);
154 * We could just take the "tracedata" index into the .tracedata
155 * section instead. Generating a hash of the data gives us a
156 * chance to work across kernel versions, and perhaps more
157 * importantly it also gives us valid/invalid check (ie we will
158 * likely not give totally bogus reports - if the hash matches,
159 * it's not any guarantee, but it's a high _likelihood_ that
160 * the match is valid).
162 void generate_pm_trace(const void *tracedata
, unsigned int user
)
164 unsigned short lineno
= *(unsigned short *)tracedata
;
165 const char *file
= *(const char **)(tracedata
+ 2);
166 unsigned int user_hash_value
, file_hash_value
;
168 user_hash_value
= user
% USERHASH
;
169 file_hash_value
= hash_string(lineno
, file
, FILEHASH
);
170 set_magic_time(user_hash_value
, file_hash_value
, dev_hash_value
);
172 EXPORT_SYMBOL(generate_pm_trace
);
174 extern char __tracedata_start
[], __tracedata_end
[];
175 static int show_file_hash(unsigned int value
)
181 for (tracedata
= __tracedata_start
; tracedata
< __tracedata_end
;
182 tracedata
+= 2 + sizeof(unsigned long)) {
183 unsigned short lineno
= *(unsigned short *)tracedata
;
184 const char *file
= *(const char **)(tracedata
+ 2);
185 unsigned int hash
= hash_string(lineno
, file
, FILEHASH
);
188 pr_info(" hash matches %s:%u\n", file
, lineno
);
194 static int show_dev_hash(unsigned int value
)
197 struct list_head
*entry
;
200 entry
= dpm_list
.prev
;
201 while (entry
!= &dpm_list
) {
202 struct device
* dev
= to_device(entry
);
203 unsigned int hash
= hash_string(DEVSEED
, dev_name(dev
), DEVHASH
);
205 dev_info(dev
, "hash matches\n");
214 static unsigned int hash_value_early_read
;
216 int show_trace_dev_match(char *buf
, size_t size
)
218 unsigned int value
= hash_value_early_read
/ (USERHASH
* FILEHASH
);
220 struct list_head
*entry
;
223 * It's possible that multiple devices will match the hash and we can't
224 * tell which is the culprit, so it's best to output them all.
227 entry
= dpm_list
.prev
;
228 while (size
&& entry
!= &dpm_list
) {
229 struct device
*dev
= to_device(entry
);
230 unsigned int hash
= hash_string(DEVSEED
, dev_name(dev
),
233 int len
= snprintf(buf
, size
, "%s\n",
234 dev_driver_string(dev
));
248 pm_trace_notify(struct notifier_block
*nb
, unsigned long mode
, void *_unused
)
251 case PM_POST_HIBERNATION
:
252 case PM_POST_SUSPEND
:
253 if (pm_trace_rtc_abused
) {
254 pm_trace_rtc_abused
= false;
255 pr_warn("Possible incorrect RTC due to pm_trace, please use 'ntpdate' or 'rdate' to reset it.\n");
264 static struct notifier_block pm_trace_nb
= {
265 .notifier_call
= pm_trace_notify
,
268 static int early_resume_init(void)
270 hash_value_early_read
= read_magic_time();
271 register_pm_notifier(&pm_trace_nb
);
275 static int late_resume_init(void)
277 unsigned int val
= hash_value_early_read
;
278 unsigned int user
, file
, dev
;
280 user
= val
% USERHASH
;
281 val
= val
/ USERHASH
;
282 file
= val
% FILEHASH
;
283 val
= val
/ FILEHASH
;
284 dev
= val
/* % DEVHASH */;
286 pr_info(" Magic number: %d:%d:%d\n", user
, file
, dev
);
287 show_file_hash(file
);
292 core_initcall(early_resume_init
);
293 late_initcall(late_resume_init
);