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Diffstat (limited to 'Documentation/power/states.txt')
| -rw-r--r-- | Documentation/power/states.txt | 62 |
1 files changed, 40 insertions, 22 deletions
diff --git a/Documentation/power/states.txt b/Documentation/power/states.txt index 50f3ef9177c1..8a39ce45d8a0 100644 --- a/Documentation/power/states.txt +++ b/Documentation/power/states.txt @@ -8,25 +8,43 @@ for each state. The states are represented by strings that can be read or written to the /sys/power/state file. Those strings may be "mem", "standby", "freeze" and -"disk", where the last one always represents hibernation (Suspend-To-Disk) and -the meaning of the remaining ones depends on the relative_sleep_states command -line argument. - -For relative_sleep_states=1, the strings "mem", "standby" and "freeze" label the -available non-hibernation sleep states from the deepest to the shallowest, -respectively. In that case, "mem" is always present in /sys/power/state, -because there is at least one non-hibernation sleep state in every system. If -the given system supports two non-hibernation sleep states, "standby" is present -in /sys/power/state in addition to "mem". If the system supports three -non-hibernation sleep states, "freeze" will be present in /sys/power/state in -addition to "mem" and "standby". - -For relative_sleep_states=0, which is the default, the following descriptions -apply. - -state: Suspend-To-Idle +"disk", where the last three always represent Power-On Suspend (if supported), +Suspend-To-Idle and hibernation (Suspend-To-Disk), respectively. + +The meaning of the "mem" string is controlled by the /sys/power/mem_sleep file. +It contains strings representing the available modes of system suspend that may +be triggered by writing "mem" to /sys/power/state. These modes are "s2idle" +(Suspend-To-Idle), "shallow" (Power-On Suspend) and "deep" (Suspend-To-RAM). +The "s2idle" mode is always available, while the other ones are only available +if supported by the platform (if not supported, the strings representing them +are not present in /sys/power/mem_sleep). The string representing the suspend +mode to be used subsequently is enclosed in square brackets. Writing one of +the other strings present in /sys/power/mem_sleep to it causes the suspend mode +to be used subsequently to change to the one represented by that string. + +Consequently, there are two ways to cause the system to go into the +Suspend-To-Idle sleep state. The first one is to write "freeze" directly to +/sys/power/state. The second one is to write "s2idle" to /sys/power/mem_sleep +and then to wrtie "mem" to /sys/power/state. Similarly, there are two ways +to cause the system to go into the Power-On Suspend sleep state (the strings to +write to the control files in that case are "standby" or "shallow" and "mem", +respectively) if that state is supported by the platform. In turn, there is +only one way to cause the system to go into the Suspend-To-RAM state (write +"deep" into /sys/power/mem_sleep and "mem" into /sys/power/state). + +The default suspend mode (ie. the one to be used without writing anything into +/sys/power/mem_sleep) is either "deep" (if Suspend-To-RAM is supported) or +"s2idle", but it can be overridden by the value of the "mem_sleep_default" +parameter in the kernel command line. On some ACPI-based systems, depending on +the information in the FADT, the default may be "s2idle" even if Suspend-To-RAM +is supported. + +The properties of all of the sleep states are described below. + + +State: Suspend-To-Idle ACPI state: S0 -Label: "freeze" +Label: "s2idle" ("freeze") This state is a generic, pure software, light-weight, system sleep state. It allows more energy to be saved relative to runtime idle by freezing user @@ -35,13 +53,13 @@ lower-power than available at run time), such that the processors can spend more time in their idle states. This state can be used for platforms without Power-On Suspend/Suspend-to-RAM -support, or it can be used in addition to Suspend-to-RAM (memory sleep) -to provide reduced resume latency. It is always supported. +support, or it can be used in addition to Suspend-to-RAM to provide reduced +resume latency. It is always supported. State: Standby / Power-On Suspend ACPI State: S1 -Label: "standby" +Label: "shallow" ("standby") This state, if supported, offers moderate, though real, power savings, while providing a relatively low-latency transition back to a working system. No @@ -58,7 +76,7 @@ state. State: Suspend-to-RAM ACPI State: S3 -Label: "mem" +Label: "deep" This state, if supported, offers significant power savings as everything in the system is put into a low-power state, except for memory, which should be placed |