/*
   * 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/export.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);
  	pr_info("RTC time: %2d:%02d:%02d, date: %02d/%02d/%02d
  ",
  		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_name(dev), 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;
  		pr_info("  hash matches %s:%u
  ", file, lineno);
  		match++;
  	}
  	return match;
  }
  
  static int show_dev_hash(unsigned int value)
  {
  	int match = 0;
  	struct list_head *entry;
  
  	device_pm_lock();
  	entry = dpm_list.prev;
  	while (entry != &dpm_list) {
  		struct device * dev = to_device(entry);
  		unsigned int hash = hash_string(DEVSEED, dev_name(dev), DEVHASH);
  		if (hash == value) {
  			dev_info(dev, "hash matches
  ");
  			match++;
  		}
  		entry = entry->prev;
  	}
  	device_pm_unlock();
  	return match;
  }
  
  static unsigned int hash_value_early_read;
  
  int show_trace_dev_match(char *buf, size_t size)
  {
  	unsigned int value = hash_value_early_read / (USERHASH * FILEHASH);
  	int ret = 0;
  	struct list_head *entry;
  
  	/*
  	 * It's possible that multiple devices will match the hash and we can't
  	 * tell which is the culprit, so it's best to output them all.
  	 */
  	device_pm_lock();
  	entry = dpm_list.prev;
  	while (size && entry != &dpm_list) {
  		struct device *dev = to_device(entry);
  		unsigned int hash = hash_string(DEVSEED, dev_name(dev),
  						DEVHASH);
  		if (hash == value) {
  			int len = snprintf(buf, size, "%s
  ",
  					    dev_driver_string(dev));
  			if (len > size)
  				len = size;
  			buf += len;
  			ret += len;
  			size -= len;
  		}
  		entry = entry->prev;
  	}
  	device_pm_unlock();
  	return ret;
  }
  
  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 */;
  
  	pr_info("  Magic number: %d:%d:%d
  ", user, file, dev);
  	show_file_hash(file);
  	show_dev_hash(dev);
  	return 0;
  }
  
  core_initcall(early_resume_init);
  late_initcall(late_resume_init);