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

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Date:	Sun, 7 Dec 2008 08:34:43 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Arjan van de Ven <arjan@...radead.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Takashi Iwai <tiwai@...e.de>, Greg KH <greg@...ah.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [linux-pm] [PATCH 1/3] PCI: Rework default handling of suspend
 and resume

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 
handler).

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.

			Linus
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