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diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
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+++ b/Documentation/ABI/testing/sysfs-power
@@ -99,9 +99,38 @@ Description:
dmesg -s 1000000 | grep 'hash matches'
+ If you do not get any matches (or they appear to be false
+ positives), it is possible that the last PM event point
+ referred to a device created by a loadable kernel module. In
+ this case cat /sys/power/pm_trace_dev_match (see below) after
+ your system is started up and the kernel modules are loaded.
+
CAUTION: Using it will cause your machine's real-time (CMOS)
clock to be set to a random invalid time after a resume.
+What; /sys/power/pm_trace_dev_match
+Date: October 2010
+Contact: James Hogan <james@albanarts.com>
+Description:
+ The /sys/power/pm_trace_dev_match file contains the name of the
+ device associated with the last PM event point saved in the RTC
+ across reboots when pm_trace has been used. More precisely it
+ contains the list of current devices (including those
+ registered by loadable kernel modules since boot) which match
+ the device hash in the RTC at boot, with a newline after each
+ one.
+
+ The advantage of this file over the hash matches printed to the
+ kernel log (see /sys/power/pm_trace), is that it includes
+ devices created after boot by loadable kernel modules.
+
+ Due to the small hash size necessary to fit in the RTC, it is
+ possible that more than one device matches the hash, in which
+ case further investigation is required to determine which
+ device is causing the problem. Note that genuine RTC clock
+ values (such as when pm_trace has not been used), can still
+ match a device and output it's name here.
+
What: /sys/power/pm_async
Date: January 2009
Contact: Rafael J. Wysocki <rjw@sisk.pl>