From: Mark Brown <broonie@opensource.wolfsonmicro.com>
To: john stultz <johnstul@us.ibm.com>
Cc: rtc-linux@googlegroups.com, LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Alessandro Zummo <a.zummo@towertech.it>,
Marcelo Roberto Jimenez <mroberto@cpti.cetuc.puc-rio.br>
Subject: Re: [rtc-linux] [PATCH 04/10] RTC: Cleanup rtc_class_ops->read_alarm()
Date: Tue, 22 Feb 2011 20:00:46 +0000 [thread overview]
Message-ID: <20110222200046.GD31611@opensource.wolfsonmicro.com> (raw)
In-Reply-To: <1298404268.9215.39.camel@work-vm>
On Tue, Feb 22, 2011 at 11:51:08AM -0800, john stultz wrote:
> On Tue, 2011-02-22 at 10:16 -0800, Mark Brown wrote:
> > The WM83xx RTCs can do this (the alarm can be used to initiate a boot)
> > and I'd expect many embedded RTC controllers can do similar. The
> > application would manage this by owning the RTC in the system, usually
> > with a configuration saying something like "boot every day at 7am" or
> > something.
> So since the RTC_ALM_SET doesn't support wildcards, the application
> would be checking the hardware at least once a day and making sure the
> alarm was properly set for 7am?
Probably, yes. Though some RTCs just ignore the day anyway.
> Does the approach I mentioned in my last mail to Marcelo sound like a
> reasonable solution?
> Basically: The kernel will try to init the value returned from
> RTC_ALM_READ to whatever the hardware has stored, but since many (very
> common) rtc devices don't support persistent values after reset,
> applications shouldn't trust that alarms will persist across resets.
That'll probably work, yes.
> > Having thought about this a bit I'm thinking that this sort of alarm
> > handling is probably something I'd expect to see handled in userspace.
> > I can see us providing a virtual RTC driver that can generate alarms
> > when there's no actual RTC hardware but adding additional functionality
> > on top of the hardware feels like an application issue.
> If you're suggesting that the multiplexing of RTC events doesn't belong
> in the kernel, and instead should be handled through userland
> coordination, then I disagree. The kernel's job is explicitly to
> abstract the hardware so that resources can be shared safely. So
> abstracting the RTC alarms doesn't seem to be overreaching. But maybe
> I'm misunderstanding what your saying?
I'm saying that for something like this it doesn't seem like the kernel
should be adding support for features that the hardware doesn't actually
have, it feels like it's going to be more complicated and error prone to
implement in kernel space.
next prev parent reply other threads:[~2011-02-22 20:00 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-21 23:55 [PATCH 00/10] [RFC] RTC: Cleanups for 2.6.39 John Stultz
2011-02-21 23:55 ` [PATCH 01/10] RTC: Cleanup rtc_class_ops->irq_set_state John Stultz
2011-02-21 23:55 ` [PATCH 02/10] RTC: Cleanup rtc_class_ops->irq_set_freq() John Stultz
2011-02-21 23:55 ` [PATCH 03/10] RTC: Cleanup rtc_class_ops->update_irq_enable() John Stultz
2011-02-21 23:55 ` [PATCH 04/10] RTC: Cleanup rtc_class_ops->read_alarm() John Stultz
2011-02-22 2:34 ` [rtc-linux] " Mark Brown
2011-02-22 2:55 ` John Stultz
2011-02-22 8:09 ` john stultz
2011-02-22 12:51 ` Marcelo Roberto Jimenez
2011-02-22 19:35 ` john stultz
2011-02-22 19:51 ` Mark Brown
2011-02-22 19:58 ` john stultz
2011-02-22 21:26 ` Marcelo Roberto Jimenez
2011-02-22 18:16 ` Mark Brown
2011-02-22 19:51 ` john stultz
2011-02-22 20:00 ` Mark Brown [this message]
2011-02-22 20:22 ` john stultz
2011-02-22 21:05 ` Mark Brown
2011-02-22 21:21 ` john stultz
2011-02-22 21:27 ` Thomas Gleixner
2011-02-22 21:40 ` Mark Brown
2011-02-22 21:33 ` Mark Brown
2011-02-22 22:10 ` john stultz
2011-02-22 23:07 ` Mark Brown
2011-02-22 19:53 ` john stultz
2011-02-22 20:31 ` Mark Brown
2011-02-21 23:55 ` [PATCH 05/10] RTC: Clean out UIE icotl implementations John Stultz
2011-02-21 23:55 ` [PATCH 06/10] RTC: Include information about UIE and PIE in RTC driver proc John Stultz
2011-02-21 23:55 ` [PATCH 07/10] RTC: Remove UIE and PIE information from the sa1100 " John Stultz
2011-02-21 23:55 ` [PATCH 08/10] RTC: Fix the cross interrupt issue on rtc-test John Stultz
2011-02-21 23:55 ` [PATCH 09/10] RTC: sa1100: Update the sa1100 RTC driver John Stultz
2011-02-21 23:55 ` [PATCH 10/10] RTC: Fix up rtc.txt documentation to reflect changes to generic rtc layer John Stultz
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