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Diffstat (limited to 'Documentation/power/states.txt')
| -rw-r--r-- | Documentation/power/states.txt | 30 |
1 files changed, 17 insertions, 13 deletions
diff --git a/Documentation/power/states.txt b/Documentation/power/states.txt index 4416b28630df..442d43df9b25 100644 --- a/Documentation/power/states.txt +++ b/Documentation/power/states.txt @@ -2,12 +2,26 @@ System Power Management States -The kernel supports three power management states generically, though -each is dependent on platform support code to implement the low-level -details for each state. This file describes each state, what they are +The kernel supports four power management states generically, though +one is generic and the other three are dependent on platform support +code to implement the low-level details for each state. +This file describes each state, what they are commonly called, what ACPI state they map to, and what string to write to /sys/power/state to enter that state +state: Freeze / Low-Power Idle +ACPI state: S0 +String: "freeze" + +This state is a generic, pure software, light-weight, low-power state. +It allows more energy to be saved relative to idle by freezing user +space and putting all I/O devices into low-power states (possibly +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 Standby/Suspend-to-RAM +support, or it can be used in addition to Suspend-to-RAM (memory sleep) +to provide reduced resume latency. + State: Standby / Power-On Suspend ACPI State: S1 @@ -22,9 +36,6 @@ We try to put devices in a low-power state equivalent to D1, which also offers low power savings, but low resume latency. Not all devices support D1, and those that don't are left on. -A transition from Standby to the On state should take about 1-2 -seconds. - State: Suspend-to-RAM ACPI State: S3 @@ -42,9 +53,6 @@ transition back to the On state. For at least ACPI, STR requires some minimal boot-strapping code to resume the system from STR. This may be true on other platforms. -A transition from Suspend-to-RAM to the On state should take about -3-5 seconds. - State: Suspend-to-disk ACPI State: S4 @@ -74,7 +82,3 @@ low-power state (like ACPI S4), or it may simply power down. Powering down offers greater savings, and allows this mechanism to work on any system. However, entering a real low-power state allows the user to trigger wake up events (e.g. pressing a key or opening a laptop lid). - -A transition from Suspend-to-Disk to the On state should take about 30 -seconds, though it's typically a bit more with the current -implementation. |