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authorRafael J. Wysocki <rjw@sisk.pl>2006-09-25 23:32:58 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-26 08:49:04 -0700
commitc5c6ba4e08ab9c9e390a0f3a7d9a5c332f5cc6ef (patch)
tree4e13a9eebd8f3901dcc187c585369ef843d1e1a7 /Documentation
parent7d145aa3abf4d96c91f37c012facd5cfbb9010d1 (diff)
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[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>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/power/interface.txt15
1 files changed, 15 insertions, 0 deletions
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 @@ 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.
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