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.
 
                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.