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Commit c5c6ba4e authored by Rafael J. Wysocki's avatar Rafael J. Wysocki Committed by Linus Torvalds
Browse files

[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: default avatarRafael J. Wysocki <rjw@sisk.pl>
Acked-by: default avatarPavel Machek <pavel@ucw.cz>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 7d145aa3

Documentation/power/interface.txt

+15 −0
Original line number Diff line number Diff line
@@ -52,3 +52,18 @@ suspend image will be as small as possible. 


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.

include/linux/resume-trace.h

+14 −10
Original line number Diff line number Diff line
@@ -3,12 +3,15 @@ 


#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 {					\

	if (pm_trace_enabled) {					\

		void *tracedata;				\

		asm volatile("movl $1f,%0\n"			\

			".section .tracedata,\"a\"\n"		\
@@ -18,6 +21,7 @@ extern void generate_resume_trace(void *tracedata, unsigned int user); 
			:"=r" (tracedata)			\

			: "i" (__LINE__), "i" (__FILE__));	\

		generate_resume_trace(tracedata, user);		\

	}							\

} while (0)



#else

kernel/power/main.c

+30 −0
Original line number Diff line number Diff line
@@ -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 @@ static ssize_t state_store(struct subsystem * subsys, const char * buf, size_t n 


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,