1.. SPDX-License-Identifier: GPL-2.0
2
3===========================
4Low Power Idle Table (LPIT)
5===========================
6
7To enumerate platform Low Power Idle states, Intel platforms are using
8“Low Power Idle Table” (LPIT). More details about this table can be
9downloaded from:
10http://www.uefi.org/sites/default/files/resources/Intel_ACPI_Low_Power_S0_Idle.pdf
11
12Residencies for each low power state can be read via FFH
13(Function fixed hardware) or a memory mapped interface.
14
15On platforms supporting S0ix sleep states, there can be two types of
16residencies:
17
18  - CPU PKG C10 (Read via FFH interface)
19  - Platform Controller Hub (PCH) SLP_S0 (Read via memory mapped interface)
20
21The following attributes are added dynamically to the cpuidle
22sysfs attribute group::
23
24  /sys/devices/system/cpu/cpuidle/low_power_idle_cpu_residency_us
25  /sys/devices/system/cpu/cpuidle/low_power_idle_system_residency_us
26
27The "low_power_idle_cpu_residency_us" attribute shows time spent
28by the CPU package in PKG C10
29
30The "low_power_idle_system_residency_us" attribute shows SLP_S0
31residency, or system time spent with the SLP_S0# signal asserted.
32This is the lowest possible system power state, achieved only when CPU is in
33PKG C10 and all functional blocks in PCH are in a low power state.
34