diff options
Diffstat (limited to 'Documentation/power/interface.txt')
| -rw-r--r-- | Documentation/power/interface.txt | 67 |
1 files changed, 44 insertions, 23 deletions
diff --git a/Documentation/power/interface.txt b/Documentation/power/interface.txt index 4117802af0f..f1f0f59a7c4 100644 --- a/Documentation/power/interface.txt +++ b/Documentation/power/interface.txt @@ -7,8 +7,8 @@ running. The interface exists in /sys/power/ directory (assuming sysfs is mounted at /sys). /sys/power/state controls system power state. Reading from this file -returns what states are supported, which is hard-coded to 'standby' -(Power-On Suspend), 'mem' (Suspend-to-RAM), and 'disk' +returns what states are supported, which is hard-coded to 'freeze', +'standby' (Power-On Suspend), 'mem' (Suspend-to-RAM), and 'disk' (Suspend-to-Disk). Writing to this file one of those strings causes the system to @@ -18,28 +18,34 @@ states. /sys/power/disk controls the operating mode of the suspend-to-disk -mechanism. Suspend-to-disk can be handled in several ways. The -greatest distinction is who writes memory to disk - the firmware or -the kernel. If the firmware does it, we assume that it also handles -suspending the system. - -If the kernel does it, then we have three options for putting the system -to sleep - using the platform driver (e.g. ACPI or other PM -registers), powering off the system or rebooting the system (for -testing). The system will support either 'firmware' or 'platform', and -that is known a priori. But, the user may choose 'shutdown' or -'reboot' as alternatives. - -Reading from this file will display what the mode is currently set -to. Writing to this file will accept one of - - 'firmware' - 'platform' +mechanism. Suspend-to-disk can be handled in several ways. We have a +few options for putting the system to sleep - using the platform driver +(e.g. ACPI or other suspend_ops), powering off the system or rebooting the +system (for testing). + +Additionally, /sys/power/disk can be used to turn on one of the two testing +modes of the suspend-to-disk mechanism: 'testproc' or 'test'. If the +suspend-to-disk mechanism is in the 'testproc' mode, writing 'disk' to +/sys/power/state will cause the kernel to disable nonboot CPUs and freeze +tasks, wait for 5 seconds, unfreeze tasks and enable nonboot CPUs. If it is +in the 'test' mode, writing 'disk' to /sys/power/state will cause the kernel +to disable nonboot CPUs and freeze tasks, shrink memory, suspend devices, wait +for 5 seconds, resume devices, unfreeze tasks and enable nonboot CPUs. Then, +we are able to look in the log messages and work out, for example, which code +is being slow and which device drivers are misbehaving. + +Reading from this file will display all supported modes and the currently +selected one in brackets, for example + + [shutdown] reboot test testproc + +Writing to this file will accept one of + + 'platform' (only if the platform supports it) 'shutdown' 'reboot' - -It will only change to 'firmware' or 'platform' if the system supports -it. + 'testproc' + 'test' /sys/power/image_size controls the size of the image created by the suspend-to-disk mechanism. It can be written a string @@ -51,4 +57,19 @@ smallest image possible. In particular, if "0" is written to this file, the 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. +is set to 2/5 of available RAM 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. |