| David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame^] | 1 | .. SPDX-License-Identifier: GPL-2.0 |
| 2 | |
| 3 | =========================== |
| 4 | Low Power Idle Table (LPIT) |
| 5 | =========================== |
| 6 | |
| 7 | To enumerate platform Low Power Idle states, Intel platforms are using |
| 8 | “Low Power Idle Table” (LPIT). More details about this table can be |
| 9 | downloaded from: |
| 10 | http://www.uefi.org/sites/default/files/resources/Intel_ACPI_Low_Power_S0_Idle.pdf |
| 11 | |
| 12 | Residencies for each low power state can be read via FFH |
| 13 | (Function fixed hardware) or a memory mapped interface. |
| 14 | |
| 15 | On platforms supporting S0ix sleep states, there can be two types of |
| 16 | residencies: |
| 17 | |
| 18 | - CPU PKG C10 (Read via FFH interface) |
| 19 | - Platform Controller Hub (PCH) SLP_S0 (Read via memory mapped interface) |
| 20 | |
| 21 | The following attributes are added dynamically to the cpuidle |
| 22 | sysfs 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 | |
| 27 | The "low_power_idle_cpu_residency_us" attribute shows time spent |
| 28 | by the CPU package in PKG C10 |
| 29 | |
| 30 | The "low_power_idle_system_residency_us" attribute shows SLP_S0 |
| 31 | residency, or system time spent with the SLP_S0# signal asserted. |
| 32 | This is the lowest possible system power state, achieved only when CPU is in |
| 33 | PKG C10 and all functional blocks in PCH are in a low power state. |