[PATCH v4 5/5] x86/umwait: Document umwait control sysfs interfaces

[Fenghua Yu <fenghua.yu@intel.com>]

Since two new sysfs interface files are created for umwait control, add
an ABI document entry for the files:
	/sys/devices/system/cpu/umwait_control/enable_c02
	/sys/devices/system/cpu/umwait_control/max_time

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
---
 .../ABI/testing/sysfs-devices-system-cpu      | 21 +++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 1528239f69b2..d22cdadd3161 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -538,3 +538,24 @@ Description:	Intel Energy and Performance Bias Hint (EPB)
 
 		This attribute is present for all online CPUs supporting the
 		Intel EPB feature.
+
+What:		/sys/devices/system/cpu/umwait_control
+		/sys/devices/system/cpu/umwait_control/enable_c02
+		/sys/devices/system/cpu/umwait_control/max_time
+Date:		May 2019
+Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
+Description:	Umwait control
+
+		enable_c02: Read/write interface to control umwait C0.2 state
+			Read returns C0.2 state status:
+				0: C0.2 is disabled
+				1: C0.2 is enabled
+
+			Write 'Yy1' or [oO][nN] for on to enable C0.2 state.
+			Write 'Nn0' or [oO][fF] for off to disable C0.2 state.
+
+		max_time: Read/write interface to control umwait maximum time
+			  in TSC-quanta that the CPU can reside in either C0.1
+			  or C0.2 state. The time is an unsigned 32-bit number.
+			  Note that a value of zero means there is no limit.
+			  Low order two bits must be zero.
-- 
2.19.1