linux-kernel - Re: [linux-pm] [RFC, PATCHv3 3/3] mmc: sdhci: handle wake-up from runtime

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Date:	Tue, 1 Mar 2011 21:48:37 +0100
From:	Pierre Tardy <tardyp@...il.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	linux-mmc@...r.kernel.org
Subject: Re: [linux-pm] [RFC, PATCHv3 3/3] mmc: sdhci: handle wake-up from runtime_pm

On Tue, Mar 1, 2011 at 9:27 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Tue, 1 Mar 2011, Pierre Tardy wrote:
>
>> >> +     if (pm_runtime_suspended()) {
>> >> +             host->waking_up = 1;
>> >> +             /* Note that we disable temporarly the interrupt until we do the
>> >> +              * resume. If we don't then we'll get constantly interrupted
>> >> +              * until we actually resume.
>> >> +              *
>> >> +              * as the irq is shared, this might not be very friendly to our
>> >> +              * irq sharers but the pm_runtime workqueue should really be
>> >> +              * called soon.
>> >
>> > Instead of disabling the IRQ, would it be possible to tell the device
>> > to stop generating an interrupt request?
>>
>> Well, the device is power gated, so any access to it will cause a bus
>> timeout (depending of the platform)
>
> But could you gate the power back on and then turn off the interrupt
> request?
That's the role of runtime_resume... On some platform, this may need
up to sending some SPI commands to the PMIC, to get those power rails
back on.
Something that you cannot do in interrupt context.

>
> It seems like a foolish design to have an interrupt request that can't
> be turned off by an interrupt handler.
It's what we have for now ( looks like I need to go back to my system
architects to see if we can change that...)

Alan,
thanks for all this feedback. I have now a much more clear view on how
this is working on ACPI, I'll try to see how we can mimic this
behaviour on intel_mid.
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