[PATCH] PM: Add pm_trace switch
Add the pm_trace attribute in /sys/power which has to be explicitly set to
one to really enable the "PM tracing" code compiled in when CONFIG_PM_TRACE
is set (which modifies the machine's CMOS clock in unpredictable ways).
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/Documentation/power/interface.txt b/Documentation/power/interface.txt
index 4117802..a66bec2 100644
--- a/Documentation/power/interface.txt
+++ b/Documentation/power/interface.txt
@@ -52,3 +52,18 @@
Reading from this file will display the current image size limit, which
is set to 500 MB by default.
+
+/sys/power/pm_trace controls the code which saves the last PM event point in
+the RTC across reboots, so that you can debug a machine that just hangs
+during suspend (or more commonly, during resume). Namely, the RTC is only
+used to save the last PM event point if this file contains '1'. Initially it
+contains '0' which may be changed to '1' by writing a string representing a
+nonzero integer into it.
+
+To use this debugging feature you should attempt to suspend the machine, then
+reboot it and run
+
+ dmesg -s 1000000 | grep 'hash matches'
+
+CAUTION: Using it will cause your machine's real-time (CMOS) clock to be
+set to a random invalid time after a resume.
diff --git a/include/linux/resume-trace.h b/include/linux/resume-trace.h
index a376bd4..81e9299 100644
--- a/include/linux/resume-trace.h
+++ b/include/linux/resume-trace.h
@@ -3,21 +3,25 @@
#ifdef CONFIG_PM_TRACE
+extern int pm_trace_enabled;
+
struct device;
extern void set_trace_device(struct device *);
extern void generate_resume_trace(void *tracedata, unsigned int user);
#define TRACE_DEVICE(dev) set_trace_device(dev)
-#define TRACE_RESUME(user) do { \
- void *tracedata; \
- asm volatile("movl $1f,%0\n" \
- ".section .tracedata,\"a\"\n" \
- "1:\t.word %c1\n" \
- "\t.long %c2\n" \
- ".previous" \
- :"=r" (tracedata) \
- : "i" (__LINE__), "i" (__FILE__)); \
- generate_resume_trace(tracedata, user); \
+#define TRACE_RESUME(user) do { \
+ if (pm_trace_enabled) { \
+ void *tracedata; \
+ asm volatile("movl $1f,%0\n" \
+ ".section .tracedata,\"a\"\n" \
+ "1:\t.word %c1\n" \
+ "\t.long %c2\n" \
+ ".previous" \
+ :"=r" (tracedata) \
+ : "i" (__LINE__), "i" (__FILE__)); \
+ generate_resume_trace(tracedata, user); \
+ } \
} while (0)
#else
diff --git a/kernel/power/main.c b/kernel/power/main.c
index 4d40332..873228c 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -17,6 +17,7 @@
#include <linux/pm.h>
#include <linux/console.h>
#include <linux/cpu.h>
+#include <linux/resume-trace.h>
#include "power.h"
@@ -281,10 +282,39 @@
power_attr(state);
+#ifdef CONFIG_PM_TRACE
+int pm_trace_enabled;
+
+static ssize_t pm_trace_show(struct subsystem * subsys, char * buf)
+{
+ return sprintf(buf, "%d\n", pm_trace_enabled);
+}
+
+static ssize_t
+pm_trace_store(struct subsystem * subsys, const char * buf, size_t n)
+{
+ int val;
+
+ if (sscanf(buf, "%d", &val) == 1) {
+ pm_trace_enabled = !!val;
+ return n;
+ }
+ return -EINVAL;
+}
+
+power_attr(pm_trace);
+
+static struct attribute * g[] = {
+ &state_attr.attr,
+ &pm_trace_attr.attr,
+ NULL,
+};
+#else
static struct attribute * g[] = {
&state_attr.attr,
NULL,
};
+#endif /* CONFIG_PM_TRACE */
static struct attribute_group attr_group = {
.attrs = g,