/*
* drivers/base/power/trace.c
*
* Copyright (C) 2006 Linus Torvalds
*
* Trace facility for suspend/resume problems, when none of the
* devices may be working.
*/
#include <linux/resume-trace.h>
#include <linux/rtc.h>
#include <asm/rtc.h>
#include "power.h"
/*
* Horrid, horrid, horrid.
*
* It turns out that the _only_ piece of hardware that actually
* keeps its value across a hard boot (and, more importantly, the
* POST init sequence) is literally the realtime clock.
*
* Never mind that an RTC chip has 114 bytes (and often a whole
* other bank of an additional 128 bytes) of nice SRAM that is
* _designed_ to keep data - the POST will clear it. So we literally
* can just use the few bytes of actual time data, which means that
* we're really limited.
*
* It means, for example, that we can't use the seconds at all
* (since the time between the hang and the boot might be more
* than a minute), and we'd better not depend on the low bits of
* the minutes either.
*
* There are the wday fields etc, but I wouldn't guarantee those
* are dependable either. And if the date isn't valid, either the
* hw or POST will do strange things.
*
* So we're left with:
* - year: 0-99
* - month: 0-11
* - day-of-month: 1-28
* - hour: 0-23
* - min: (0-30)*2
*
* Giving us a total range of 0-16128000 (0xf61800), ie less
* than 24 bits of actual data we can save across reboots.
*
* And if your box can't boot in less than three minutes,
* you're screwed.
*
* Now, almost 24 bits of data is pitifully small, so we need
* to be pretty dense if we want to use it for anything nice.
* What we do is that instead of saving off nice readable info,
* we save off _hashes_ of information that we can hopefully
* regenerate after the reboot.
*
* In particular, this means that we might be unlucky, and hit
* a case where we have a hash collision, and we end up not
* being able to tell for certain exactly which case happened.
* But that's hopefully unlikely.
*
* What we do is to take the bits we can fit, and split them
* into three parts (16*997*1009 = 16095568), and use the values
* for:
* - 0-15: user-settable
* - 0-996: file + line number
* - 0-1008: device
*/
#define USERHASH (16)
#define FILEHASH (997)
#define DEVHASH (1009)
#define DEVSEED (7919)
static unsigned int dev_hash_value;
static int set_magic_time(unsigned int user, unsigned int file, unsigned int device)
{
unsigned int n = user + USERHASH*(file + FILEHASH*device);
// June 7th, 2006
static struct rtc_time time = {
.tm_sec = 0,
.tm_min = 0,
.tm_hour = 0,
.tm_mday = 7,
.tm_mon = 5, // June - counting from zero
.tm_year = 106,
.tm_wday = 3,
.tm_yday = 160,
.tm_isdst = 1
};
time.tm_year = (n % 100);
n /= 100;
time.tm_mon = (n % 12);
n /= 12;
time.tm_mday = (n % 28) + 1;
n /= 28;
time.tm_hour = (n % 24);
n /= 24;
time.tm_min = (n % 20) * 3;
n /= 20;
set_rtc_time(&time);
return n ? -1 : 0;
}
static unsigned int read_magic_time(void)
{
struct rtc_time time;
unsigned int val;
get_rtc_time(&time);
printk("Time: %2d:%02d:%02d Date: %02d/%02d/%02d\n",
time.tm_hour, time.tm_min, time.tm_sec,
time.tm_mon + 1, time.tm_mday, time.tm_year % 100);
val = time.tm_year; /* 100 years */
if (val > 100)
val -= 100;
val += time.tm_mon * 100; /* 12 months */
val += (time.tm_mday-1) * 100 * 12; /* 28 month-days */
val += time.tm_hour * 100 * 12 * 28; /* 24 hours */
val += (time.tm_min / 3) * 100 * 12 * 28 * 24; /* 20 3-minute intervals */
return val;
}
/*
* This is just the sdbm hash function with a user-supplied
* seed and final size parameter.
*/
static unsigned int hash_string(unsigned int seed, const char *data, unsigned int mod)
{
unsigned char c;
while ((c = *data++) != 0) {
seed = (seed << 16) + (seed << 6) - seed + c;
}
return seed % mod;
}
void set_trace_device(struct device *dev)
{
dev_hash_value = hash_string(DEVSEED, dev->bus_id, DEVHASH);
}
EXPORT_SYMBOL(set_trace_device);
/*
* We could just take the "tracedata" index into the .tracedata
* section instead. Generating a hash of the data gives us a
* chance to work across kernel versions, and perhaps more
* importantly it also gives us valid/invalid check (ie we will
* likely not give totally bogus reports - if the hash matches,
* it's not any guarantee, but it's a high _likelihood_ that
* the match is valid).
*/
void generate_resume_trace(const void *tracedata, unsigned int user)
{
unsigned short lineno = *(unsigned short *)tracedata;
const char *file = *(const char **)(tracedata + 2);
unsigned int user_hash_value, file_hash_value;
user_hash_value = user % USERHASH;
file_hash_value = hash_string(lineno, file, FILEHASH);
set_magic_time(user_hash_value, file_hash_value, dev_hash_value);
}
EXPORT_SYMBOL(generate_resume_trace);
extern char __tracedata_start, __tracedata_end;
static int show_file_hash(unsigned int value)
{
int match;
char *tracedata;
match = 0;
for (tracedata = &__tracedata_start ; tracedata < &__tracedata_end ;
tracedata += 2 + sizeof(unsigned long)) {
unsigned short lineno = *(unsigned short *)tracedata;
const char *file = *(const char **)(tracedata + 2);
unsigned int hash = hash_string(lineno, file, FILEHASH);
if (hash != value)
continue;
printk(" hash matches %s:%u\n", file, lineno);
match++;
}
return match;
}
static int show_dev_hash(unsigned int value)
{
int match = 0;
struct list_head * entry = dpm_active.prev;
while (entry != &dpm_active) {
struct device * dev = to_device(entry);
unsigned int hash = hash_string(DEVSEED, dev->bus_id, DEVHASH);
if (hash == value) {
printk(" hash matches device %s\n", dev->bus_id);
match++;
}
entry = entry->prev;
}
return match;
}
static unsigned int hash_value_early_read;
static int early_resume_init(void)
{
hash_value_early_read = read_magic_time();
return 0;
}
static int late_resume_init(void)
{
unsigned int val = hash_value_early_read;
unsigned int user, file, dev;
user = val % USERHASH;
val = val / USERHASH;
file = val % FILEHASH;
val = val / FILEHASH;
dev = val /* % DEVHASH */;
printk(" Magic number: %d:%d:%d\n", user, file, dev);
show_file_hash(file);
show_dev_hash(dev);
return 0;
}
core_initcall(early_resume_init);
late_initcall(late_resume_init);
