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rtc: document the sysfs interface

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The sysfs interface to the RTC class drivers is currently undocumented.
Add some basic documentation defining the semantics of the fields.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matthew Garrett 2009-09-22 16:46:31 -07:00 committed by Linus Torvalds
parent dac94d9ec9
commit ea3d1606fd
1 changed files with 22 additions and 0 deletions
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Documentation/rtc.txt
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@ -135,6 +135,28 @@ 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 the system clock from the discrete RTC, but use the integrated one for all
other tasks, because of its greater functionality. other tasks, because of its greater functionality.
SYSFS INTERFACE
---------------
The sysfs interface under /sys/class/rtc/rtcN provides access to various
rtc attributes without requiring the use of ioctls. All dates and times
are in the RTC's timezone, rather than in system time.
date: RTC-provided date
max_user_freq: The maximum interrupt rate an unprivileged user may request
from this RTC.
name: The name of the RTC corresponding to this sysfs directory
since_epoch: The number of seconds since the epoch according to the RTC
time: RTC-provided time
wakealarm: The time at which the clock will generate a system wakeup
event. This is a one shot wakeup event, so must be reset
after wake if a daily wakeup is required. Format is either
seconds since the epoch or, if there's a leading +, seconds
in the future.
IOCTL INTERFACE
---------------
The ioctl() calls supported by /dev/rtc are also supported by the RTC class The ioctl() calls supported by /dev/rtc are also supported by the RTC class
framework. However, because the chips and systems are not standardized, framework. However, because the chips and systems are not standardized,
some PC/AT functionality might not be provided. And in the same way, some some PC/AT functionality might not be provided. And in the same way, some