Re: [linux-pm] [PATCH 1/3] PCI: Rework default handling of suspendand resume

From: Linus Torvalds
Date: Sun Dec 07 2008 - 11:35:25 EST

On Sun, 7 Dec 2008, Rafael J. Wysocki wrote:
> So, can we just say that PCI drivers shouldn't free IRQs during suspend and
> request them during resume, and if there's any problem that leads to, then it
> should be solved differently?

Well, there are reasons why _individual_ drivers might want to free and
re-request irq's during suspend, so I wouldn't say it's wrong either.

For example, let's say that driver xyzzy has a suspend function (note: not
"suspend_late" or "suspend_noirq"), and that in that suspend routine it
turns off some slow part of itself (ie it doesn't go into D3, but let's
say that it's a wireless device and it turns off its radio).

And maybe that driver is written in such a way that the interrupt routine
wants to access the radio chip.

Now, the driver has two choices:

- just make the irq handler happy with the partially suspended state (and
admittedly this is likely the _sane_ choice and interrupt handlers
should always be robust, but never mind)

- or just make the suspend routine make sure that the chip doesn't
generate any interrupts, and release the interrupt handler (the latter
is needed because of shared interrupts - even if _that_ chip doesn't
generate any interrupts, the interrupt handler will still get called if
there are shared interrupts, of course)

IOW, I think an _acceptable_ solution to a problem like this is "hey, I'm
turning myself off, so I'll also turn off my interrupts and disable my irq

I just don't think it's a very -good- approach. I think it's an acceptable
one, but it sure as hell shouldn't be the _default_ one. Especially not
for a lot of simple devices that can probably do all of their save/restore
entirely inside the "noirq" window, so they would never have this kind of
issue anyway.

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