Documentation/ABI: Document umwait control sysfs interfaces

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

[ tglx: Made the write value instructions readable ]

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
Cc: "Borislav Petkov" <bp@alien8.de>
Cc: "H Peter Anvin" <hpa@zytor.com>
Cc: "Andy Lutomirski" <luto@kernel.org>
Cc: "Peter Zijlstra" <peterz@infradead.org>
Cc: "Tony Luck" <tony.luck@intel.com>
Cc: "Ravi V Shankar" <ravi.v.shankar@intel.com>
Link: https://lkml.kernel.org/r/1560994438-235698-6-git-send-email-fenghua.yu@intel.com

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 1528239f69b2fea8a2f595dac7ebd379cf97714a..923fe2001472d152ccfaa50b0eee81482928552d 100644 (file)
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -538,3 +538,26 @@ 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 'y' or '1'  or 'on' to enable C0.2 state.
+                       Write 'n' or '0'  or 'off' to disable C0.2 state.
+
+                       The interface is case insensitive.
+
+               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.