rtc: Document RTC_VL_READ and RTC_VL_CLR ioctls

RTC_VL_READ and RTC_VL_CLR have been introduced in 2012 with commit
0f20b767e20a ("drivers/rtc/rtc-pcf8563.c: add RTC_VL_READ/RTC_VL_CLR ioctl
feature")

Document them now that they have been unified.

Link: https://lore.kernel.org/r/20191214220259.621996-3-alexandre.belloni@bootlin.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

diff --git a/Documentation/ABI/testing/rtc-cdev b/Documentation/ABI/testing/rtc-cdev
index 97447283f13bf0eac96bc09cd89438ddb73e3524..25910c3c3d7eb11a44b5f527778cc8311828e911 100644 (file)
--- a/Documentation/ABI/testing/rtc-cdev
+++ b/Documentation/ABI/testing/rtc-cdev
@@ -33,6 +33,14 @@ Description:
                  Requires a separate RTC_PIE_ON call to enable the periodic
                  interrupts.
 
+               * RTC_VL_READ: Read the voltage inputs status of the RTC when
+                 supported. The value is a bit field of RTC_VL_*, giving the
+                 status of the main and backup voltages.
+
+               * RTC_VL_CLEAR: Clear the voltage status of the RTC. Some RTCs
+                 need user interaction when the backup power provider is
+                 replaced or charged to be able to clear the status.
+
                The ioctl() calls supported by the older /dev/rtc interface are
                also supported by the newer RTC class framework. However,
                because the chips and systems are not standardized, some PC/AT