Re: [PATCH 02/12] arm: omap3: Only sleep during cpu_idle if I/O wake-ups work

Mark A. Greer
2012-04-13T00:13:04Z

On Wed, Apr 11, 2012 at 06:42:44PM -0500, Jon Hunter wrote:
> Hi Mark,
>
> On 04/11/2012 02:05 PM, Mark A. Greer wrote:
> > From: "Mark A. Greer" <mgreer@animalcreek.com>
> >
> > Currently in the OMAP3 code, cpu_idle() calls pm_idle(),
> > which is a function pointer set to omap3_pm_idle()).
> > omap3_pm_idle() calls omap_sram_idle() which eventually
> > causes a 'wfi' instruction to be executed effectively
> > putting the system to sleep. It is assumed that an
> > I/O wake-up event will occur to wake the system up again.
> > This doesn't work on systems that don't support I/O wake-ups
> > (indicated by omap3_has_io_wakeup() returning false).
> >
> > Leaving pm_idle() pointing to default_idle() won't work
> > either because the cpu_<processor>_do_idle() routine which
> > is eventually called may also execute a 'wfi' instruction
> > (e.g., cpu_v7_do_idle()).
>
> So with this change you will never execute wfi?

Correct.

> I would have thought a timer or peripheral interrupt would be able to
> bring you out of wfi.

It occasionally wakes up so I'm guessing its a timer interrupt.
It seems that peripheral interrupts aren't waking it up.
Perhaps something isn't configured correctly but everything I've
looked at looks okay (AFAICT).

> IO wake-ups would only be needed for very low
> power states. At least that is how it is on OMAP devices. I am not sure
> how the AMxxx devices differ.

The am35x isn't supposed to have them so there's no real info on it
but I'm sure its the same as regular OMAP devices.

Mark
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