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Documentation: rtc: move iotcl interface documentation to ABI 

The ioctl interface should be in Documentation/ABI along with the rest
of the interfaces.

Signed-off-by: Aishwarya Pant <aishpant@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
This commit is contained in:
Aishwarya Pant 2018-01-01 23:01:24 +05:30 committed by Alexandre Belloni
parent d5bc5cde84
commit 796c0ad79e
2 changed files with 44 additions and 47 deletions
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42
Documentation/ABI/testing/rtc-cdev Normal file
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@ -0,0 +1,42 @@
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.
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.

49
Documentation/rtc.txt
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@ -136,50 +136,5 @@ a high functionality RTC is integrated into the SOC. That system might read
the system clock from the discrete RTC, but use the integrated one for all
other tasks, because of its greater functionality.
IOCTL interface
---------------
The ioctl() calls supported by /dev/rtc are also supported by the 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.
* RTC_RD_TIME, RTC_SET_TIME ... every RTC supports at least reading
time, returning the result as a Gregorian calendar date and 24 hour
wall clock time. To be most useful, this time may also be updated.
* RTC_AIE_ON, RTC_AIE_OFF, RTC_ALM_SET, RTC_ALM_READ ... when the RTC
is connected to an IRQ line, it can often issue an alarm IRQ up to
24 hours in the future. (Use RTC_WKALM_* by preference.)
* RTC_WKALM_SET, RTC_WKALM_RD ... RTCs that can issue alarms beyond
the next 24 hours use a slightly more powerful API, which supports
setting the longer alarm time and enabling its IRQ using a single
request (using the same model as EFI firmware).
* RTC_UIE_ON, RTC_UIE_OFF ... if the RTC offers IRQs, the RTC framework
will emulate this mechanism.
* RTC_PIE_ON, RTC_PIE_OFF, RTC_IRQP_SET, RTC_IRQP_READ ... these icotls
are emulated via a kernel hrtimer.
In many cases, the RTC alarm can be a system wake event, used to force
Linux out of a low power sleep state (or hibernation) back to a fully
operational state. For example, a system could enter a deep power saving
state until it's time to execute some scheduled tasks.
Note that many of these ioctls are handled by the common rtc-dev interface.
Some common examples:
* RTC_RD_TIME, RTC_SET_TIME: the read_time/set_time functions will be
called with appropriate values.
* RTC_ALM_SET, RTC_ALM_READ, RTC_WKALM_SET, RTC_WKALM_RD: gets or sets
the alarm rtc_timer. May call the set_alarm driver function.
* RTC_IRQP_SET, RTC_IRQP_READ: These are emulated by the generic code.
* RTC_PIE_ON, RTC_PIE_OFF: These are also emulated by the generic code.
If all else fails, check out the tools/testing/selftests/timers/rtctest.c test!
Check out tools/testing/selftests/timers/rtctest.c for an example usage of the
ioctl interface.