linux-kernel - Re: [PATCH] rtc: Set wakeup capability for I2C and SPI RTC drivers

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Date:	Fri, 28 Aug 2009 04:30:10 +0400
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	David Brownell <david-b@...bell.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Jean Delvare <khali@...ux-fr.org>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org,
	David Brownell <dbrownell@...rs.sourceforge.net>
Subject: Re: [PATCH] rtc: Set wakeup capability for I2C and SPI RTC drivers

On Fri, Aug 28, 2009 at 03:19:25AM +0400, Anton Vorontsov wrote:
[...]
> > That is why platform code should device_init_wakeup() and
> > drivers should check device_can_wakeup(dev) ...
> 
> They should (and do) check may_wakeup() (i.e. should_wakeup) before
> suspending, not can_wakeup().
> 
> static int ds1374_suspend(struct i2c_client *client, pm_message_t state)
> {
>         if (client->irq >= 0 && device_may_wakeup(&client->dev))
>                 enable_irq_wake(client->irq);
>         return 0;
> }
> 
> (quite funny, they issue enable_irq_wake(), assuming that otherwise
> IRQ line won't trigger CPU wakeup. But in reality, there are interrupt
> controllers that you can't control in that regard: any IRQ activity
> will always resume CPU. And so 'echo disable > /sys/.../wakeup' won't
> guarantee anything. Unreliable, nasty? Could be.)

BTW, of course we can fix this by masking interrupts before
suspending, but nobody actually do this (but should, I think).

And if RTC's IRQ is wired to power switch you're in trouble
without any way to fix this.

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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