linux-kernel - Re: [rtc-linux] [PATCH 04/10] RTC: Cleanup rtc_class_ops->read

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Message-ID: <AANLkTi=9iuFStoKZ1VZf0AMno=2LfyWqppPEReUFkEC2@mail.gmail.com>
Date:	Tue, 22 Feb 2011 18:26:34 -0300
From:	Marcelo Roberto Jimenez <mroberto@...i.cetuc.puc-rio.br>
To:	john stultz <johnstul@...ibm.com>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	rtc-linux@...glegroups.com, LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alessandro Zummo <a.zummo@...ertech.it>
Subject: Re: [rtc-linux] [PATCH 04/10] RTC: Cleanup rtc_class_ops->read_alarm()

On Tue, Feb 22, 2011 at 16:58, john stultz <johnstul@...ibm.com> wrote:
> 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.

Just a correction to my post, it was not AIE/UIE with ramdom values,
it was an alarm or update interrupt pending bit in the status register
(RTSR) that woke up set after reboot, even before interrupts were
enabled. In this case, the device would wake up with an interrupt
pending. The interrupt routine would not clear an interrupt that was
not enabled and that lead to an infinite loop of interrupts.

Regards,
Marcelo.
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