summaryrefslogtreecommitdiff
path: root/Documentation/firmware-guide
diff options
context:
space:
mode:
authorChangbin Du <changbin.du@gmail.com>2019-04-25 01:53:04 +0800
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2019-04-25 23:07:20 +0200
commit4887954cac779abe38d3ba6446dec341ccca04ea (patch)
treeab9ec6c57324c628188cad0a2911a50fd28ffd43 /Documentation/firmware-guide
parent3e57460f007c86476c376a08e31da441cae0b195 (diff)
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 <changbin.du@gmail.com> Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'Documentation/firmware-guide')
-rw-r--r--Documentation/firmware-guide/acpi/index.rst1
-rw-r--r--Documentation/firmware-guide/acpi/lpit.rst33
2 files changed, 34 insertions, 0 deletions
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.