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