Add some basic resume trace facilities

Considering that there isn't a lot of hw we can depend on during resume,
this is about as good as it gets.

This is x86-only for now, although the basic concept (and most of the
code) will certainly work on almost any platform.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 229 insertions, 0 deletions

diff --git a/drivers/base/power/Makefile b/drivers/base/power/Makefile
index ceeeba2c56c7..91f230939c1e 100644
--- a/drivers/base/power/Makefile
+++ b/drivers/base/power/Makefile
@@ -1,5 +1,6 @@
 obj-y                   := shutdown.o
 obj-$(CONFIG_PM)        += main.o suspend.o resume.o runtime.o sysfs.o
+obj-$(CONFIG_PM_TRACE)  += trace.o
 
 ifeq ($(CONFIG_DEBUG_DRIVER),y)
 EXTRA_CFLAGS += -DDEBUG
diff --git a/drivers/base/power/trace.c b/drivers/base/power/trace.c
new file mode 100644
index 000000000000..a9ab30fefffc
--- /dev/null
+++ b/drivers/base/power/trace.c
@@ -0,0 +1,228 @@
+/*
+ * 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, time.tm_mday, time.tm_year);
+        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);
+}
+
+/*
+ * 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(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);
+}
+
+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 += 6) {
+                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);