Diffstat (limited to 'Documentation/power/states.txt')
1 files changed, 17 insertions, 13 deletions
diff --git a/Documentation/power/states.txt b/Documentation/power/states.txt
index 4416b28630d..442d43df9b2 100644
@@ -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
+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
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
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