linux-kernel - Re: [RFC][PATCH -mm 3/3] PM: Disable _request

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Message-ID: <20070528165441.GA1669@srcf.ucam.org>
Date:	Mon, 28 May 2007 17:54:41 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>, Oliver Neukum <oliver@...kum.org>
Subject: Re: [RFC][PATCH -mm 3/3] PM: Disable _request_firmware before hibernation/suspend

On Mon, May 28, 2007 at 12:43:36PM -0400, Alan Stern wrote:
> On Mon, 28 May 2007, Matthew Garrett wrote:
> > On Mon, May 28, 2007 at 12:09:30PM -0400, Alan Stern wrote:
> > 
> > > I can't speak for the second example, but there's a good reason the
> > > first example works this way.  It's not a matter of races; the problem
> > > is that the kernel thread's job is to selectively suspend and resume
> > > devices.  We don't want it doing this while a system sleep is in 
> > > progress; it would (and in fact has, before the thread was made 
> > > freezable) cause the sleep transition to abort.
> > 
> > How does this work on PPC or APM systems?
> 
> For hibernation it behaves the same as on other types of systems.
> 
> For STR it generally works okay.  There was one report of suspends
> aborting, and it looked like this was caused by selective resumes
> originating from userspace.  This seemed to be unrelated to the kernel
> threads; apparently some program was running while the STR was in
> progress, and causing the problem.  For example, the lsusb program will
> do a selective resume on every USB device as it scans through them all.
> However that's just a guess, we haven't fully resolved that bug report.
> 
> The theoretical answer is that it behaves the way we want.  The kernel 
> thread does selective resumes in response to device requests.  If such 
> a request comes in while the system is asleep it will awaken the 
> system; so it's only logical that a request coming in while the system 
> is in the process of going to sleep should abort the suspend.

Ok, I guess I'm still not clear on this :) If it doesn't cause major 
problems on Powermac or APM systems, why is freezing the thread 
beneficial on ACPI systems?

-- 
Matthew Garrett | mjg59@...f.ucam.org
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