Messages in this thread | | | Subject | Re: [rtc-linux] [PATCH 04/10] RTC: Cleanup rtc_class_ops->read_alarm() | From | john stultz <> | Date | Tue, 22 Feb 2011 11:58:16 -0800 |
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On Tue, 2011-02-22 at 19:51 +0000, Mark Brown wrote: > On Tue, Feb 22, 2011 at 11:35:10AM -0800, john stultz wrote: > > > Yea. The way I thought about it originally was that you can set an alarm > > and that alarm will fire if the machine is on, suspended or even in some > > cases off. Then, when the machine is booted (system reset), the state > > of the RTC's alarm should not be trusted. > > > Your description of the AIE/UIE having random values aligns with that > > intuition. > > This seems rather worrying - it sounds like it might mean that the > device might come up firing spuriously which doesn't seem terribly > clever.
Well, in those known cases the driver should initalize the irq modes to be off.
> > However, if the expectation is that once set, the alarm should persist > > across any number of reboots, this makes it a bit more complicated. > > For an embedded device I'd expect that either nothing about the RTC > would persist (including the time) or everything would.
But that isn't the reality of the hardware. On reboot the kernel can't trust hardware to be in a valid state.
Even so, we can try to preserve what we can, but I think the expectation from an application's point of view shouldn't be that rtc device's alarm state will be valid upon reset.
thanks -john
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