0001 .. SPDX-License-Identifier: GPL-2.0
0002
0003 ===========================
0004 Low Power Idle Table (LPIT)
0005 ===========================
0006
0007 To enumerate platform Low Power Idle states, Intel platforms are using
0008 “Low Power Idle Table” (LPIT). More details about this table can be
0009 downloaded from:
0010 https://www.uefi.org/sites/default/files/resources/Intel_ACPI_Low_Power_S0_Idle.pdf
0011
0012 Residencies for each low power state can be read via FFH
0013 (Function fixed hardware) or a memory mapped interface.
0014
0015 On platforms supporting S0ix sleep states, there can be two types of
0016 residencies:
0017
0018 - CPU PKG C10 (Read via FFH interface)
0019 - Platform Controller Hub (PCH) SLP_S0 (Read via memory mapped interface)
0020
0021 The following attributes are added dynamically to the cpuidle
0022 sysfs attribute group::
0023
0024 /sys/devices/system/cpu/cpuidle/low_power_idle_cpu_residency_us
0025 /sys/devices/system/cpu/cpuidle/low_power_idle_system_residency_us
0026
0027 The "low_power_idle_cpu_residency_us" attribute shows time spent
0028 by the CPU package in PKG C10
0029
0030 The "low_power_idle_system_residency_us" attribute shows SLP_S0
0031 residency, or system time spent with the SLP_S0# signal asserted.
0032 This is the lowest possible system power state, achieved only when CPU is in
0033 PKG C10 and all functional blocks in PCH are in a low power state.
