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Documentation: rtc: move iotcl interface documentation to ABI

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

Signed-off-by: Aishwarya Pant <[email protected]>
Signed-off-by: Alexandre Belloni <[email protected]>
This commit is contained in:
Aishwarya Pant 2018-01-01 23:01:24 +05:30 • committed by Alexandre Belloni
commit 796c0ad79e
2 changed files with 44 additions and 47 deletions
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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.