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Diffstat (limited to 'Documentation/power/states.txt')
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diff --git a/Documentation/power/states.txt b/Documentation/power/states.txt deleted file mode 100644 index 4416b28630d..00000000000 --- a/Documentation/power/states.txt +++ /dev/null @@ -1,80 +0,0 @@ - -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 -commonly called, what ACPI state they map to, and what string to write -to /sys/power/state to enter that state - - -State: Standby / Power-On Suspend -ACPI State: S1 -String: "standby" - -This state offers minimal, though real, power savings, while providing -a very low-latency transition back to a working system. No operating -state is lost (the CPU retains power), so the system easily starts up -again where it left off. - -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 -String: "mem" - -This state offers significant power savings as everything in the -system is put into a low-power state, except for memory, which is -placed in self-refresh mode to retain its contents. - -System and device state is saved and kept in memory. All devices are -suspended and put into D3. In many cases, all peripheral buses lose -power when entering STR, so devices must be able to handle the -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 -String: "disk" - -This state offers the greatest power savings, and can be used even in -the absence of low-level platform support for power management. This -state operates similarly to Suspend-to-RAM, but includes a final step -of writing memory contents to disk. On resume, this is read and memory -is restored to its pre-suspend state. - -STD can be handled by the firmware or the kernel. If it is handled by -the firmware, it usually requires a dedicated partition that must be -setup via another operating system for it to use. Despite the -inconvenience, this method requires minimal work by the kernel, since -the firmware will also handle restoring memory contents on resume. - -For suspend-to-disk, a mechanism called 'swsusp' (Swap Suspend) is used -to write memory contents to free swap space. swsusp has some restrictive -requirements, but should work in most cases. Some, albeit outdated, -documentation can be found in Documentation/power/swsusp.txt. -Alternatively, userspace can do most of the actual suspend to disk work, -see userland-swsusp.txt. - -Once memory state is written to disk, the system may either enter a -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. |