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authorJohn Stultz <john.stultz@linaro.org>2011-02-21 22:58:51 -0800
committerJohn Stultz <john.stultz@linaro.org>2011-03-09 11:22:50 -0800
commitf44f7f96a20af16f6f12e1c995576d6becf5f57b (patch)
treebbe0b8bec5defed39fade13c79a1cb19b74fb6e3 /drivers/rtc/rtc-pl031.c
parenta5abba989deceb731047425812d268daf7536575 (diff)
RTC: Initialize kernel state from RTC
Mark Brown pointed out a corner case: that RTC alarms should be allowed to be persistent across reboots if the hardware supported it. The rework of the generic layer to virtualize the RTC alarm virtualized much of the alarm handling, and removed the code used to read the alarm time from the hardware. Mark noted if we want the alarm to be persistent across reboots, we need to re-read the alarm value into the virtualized generic layer at boot up, so that the generic layer properly exposes that value. This patch restores much of the earlier removed rtc_read_alarm code and wires it in so that we set the kernel's alarm value to what we find in the hardware at boot time. NOTE: Not all hardware supports persistent RTC alarm state across system reset. rtc-cmos for example will keep the alarm time, but disables the AIE mode irq. Applications should not expect the RTC alarm to be valid after a system reset. We will preserve what we can, to represent the hardware state at boot, but its not guarenteed. Further, in the future, with multiplexed RTC alarms, the soonest alarm to fire may not be the one set via the /dev/rt ioctls. So an application may set the alarm with RTC_ALM_SET, but after a reset find that RTC_ALM_READ returns an earlier time. Again, we preserve what we can, but applications should not expect the RTC alarm state to persist across a system reset. Big thanks to Mark for pointing out the issue! Thanks also to Marcelo for helping think through the solution. CC: Mark Brown <broonie@opensource.wolfsonmicro.com> CC: Marcelo Roberto Jimenez <mroberto@cpti.cetuc.puc-rio.br> CC: Thomas Gleixner <tglx@linutronix.de> CC: Alessandro Zummo <a.zummo@towertech.it> CC: rtc-linux@googlegroups.com Reported-by: Mark Brown <broonie@opensource.wolfsonmicro.com> Signed-off-by: John Stultz <john.stultz@linaro.org>
Diffstat (limited to 'drivers/rtc/rtc-pl031.c')
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