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linux-imx/Documentation/ABI/testing/rtc-cdev
Alexandre Belloni 790a19f18a rtc: Document RTC_VL_READ and RTC_VL_CLR ioctls 
RTC_VL_READ and RTC_VL_CLR have been introduced in 2012 with commit
0f20b767e2 ("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>
2019-12-18 10:37:20 +01:00

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What: /dev/rtcX Date: April 2005 KernelVersion: 2.6.12 Contact: linux-rtc@vger.kernel.org Description: The ioctl interface to drivers for real-time clocks (RTCs). Following actions are supported:

	* RTC_RD_TIME, RTC_SET_TIME: Read or set the RTC time. Time
	  format is a Gregorian calendar date and 24 hour wall clock
	  time.

	* RTC_AIE_ON, RTC_AIE_OFF: Enable or disable the alarm interrupt
	  for RTCs that support alarms

	* RTC_ALM_READ, RTC_ALM_SET: Read or set the alarm time for
	  RTCs that support alarms. Can be set upto 24 hours in the
	  future. Requires a separate RTC_AIE_ON call to enable the
	  alarm interrupt. (Prefer to use RTC_WKALM_*)

	* RTC_WKALM_RD, RTC_WKALM_SET: For RTCs that support a more
	  powerful interface, which can issue alarms beyond 24 hours and
	  enable IRQs in the same request.

	* RTC_PIE_ON, RTC_PIE_OFF: Enable or disable the periodic
	  interrupt for RTCs that support periodic interrupts.

	* RTC_UIE_ON, RTC_UIE_OFF: Enable or disable the update
	  interrupt for RTCs that support it.

	* RTC_IRQP_READ, RTC_IRQP_SET: Read or set the frequency for
	  periodic interrupts for RTCs that support periodic interrupts.
	  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
	functionality might not be provided. And in the same way, some
	newer features -- including those enabled by ACPI -- are exposed
	by the RTC class framework, but can't be supported by the older
	driver.