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| -rw-r--r-- | Documentation/acpi/lpit.txt | 25 |
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diff --git a/Documentation/acpi/lpit.txt b/Documentation/acpi/lpit.txt new file mode 100644 index 000000000..b426398d2 --- /dev/null +++ b/Documentation/acpi/lpit.txt @@ -0,0 +1,25 @@ +To enumerate platform Low Power Idle states, Intel platforms are using +“Low Power Idle Table” (LPIT). More details about this table can be +downloaded from: +http://www.uefi.org/sites/default/files/resources/Intel_ACPI_Low_Power_S0_Idle.pdf + +Residencies for each low power state can be read via FFH +(Function fixed hardware) or a memory mapped interface. + +On platforms supporting S0ix sleep states, there can be two types of +residencies: +- CPU PKG C10 (Read via FFH interface) +- Platform Controller Hub (PCH) SLP_S0 (Read via memory mapped interface) + +The following attributes are added dynamically to the cpuidle +sysfs attribute group: + /sys/devices/system/cpu/cpuidle/low_power_idle_cpu_residency_us + /sys/devices/system/cpu/cpuidle/low_power_idle_system_residency_us + +The "low_power_idle_cpu_residency_us" attribute shows time spent +by the CPU package in PKG C10 + +The "low_power_idle_system_residency_us" attribute shows SLP_S0 +residency, or system time spent with the SLP_S0# signal asserted. +This is the lowest possible system power state, achieved only when CPU is in +PKG C10 and all functional blocks in PCH are in a low power state. |