From 4887954cac779abe38d3ba6446dec341ccca04ea Mon Sep 17 00:00:00 2001 From: Changbin Du Date: Thu, 25 Apr 2019 01:53:04 +0800 Subject: Documentation: ACPI: move lpit.txt to firmware-guide/acpi and convert to reST This converts the plain text documentation to reStructuredText format and adds it to Sphinx TOC tree. No essential content change. Signed-off-by: Changbin Du Reviewed-by: Mauro Carvalho Chehab Signed-off-by: Rafael J. Wysocki --- Documentation/firmware-guide/acpi/index.rst | 1 + Documentation/firmware-guide/acpi/lpit.rst | 33 +++++++++++++++++++++++++++++ 2 files changed, 34 insertions(+) create mode 100644 Documentation/firmware-guide/acpi/lpit.rst (limited to 'Documentation/firmware-guide') diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst index fca854f017d8..0e60f4b7129a 100644 --- a/Documentation/firmware-guide/acpi/index.rst +++ b/Documentation/firmware-guide/acpi/index.rst @@ -22,3 +22,4 @@ ACPI Support gpio-properties i2c-muxes acpi-lid + lpit diff --git a/Documentation/firmware-guide/acpi/lpit.rst b/Documentation/firmware-guide/acpi/lpit.rst new file mode 100644 index 000000000000..aca928fab027 --- /dev/null +++ b/Documentation/firmware-guide/acpi/lpit.rst @@ -0,0 +1,33 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=========================== +Low Power Idle Table (LPIT) +=========================== + +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. -- cgit v1.2.3-59-g8ed1b