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

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Date:	Mon, 28 May 2007 00:01:12 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Kay Sievers" <kay.sievers@...y.org>
Cc:	"Matthew Garrett" <mjg59@...f.ucam.org>,
	"pm list" <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Nigel Cunningham" <nigel@...el.suspend2.net>,
	"Pavel Machek" <pavel@....cz>,
	"Alan Stern" <stern@...land.harvard.edu>,
	"Oliver Neukum" <oliver@...kum.org>
Subject: Re: [RFC][PATCH -mm 3/3] PM: Disable _request_firmware before hibernation/suspend

On Sunday, 27 May 2007 23:49, Kay Sievers wrote:
> On 5/27/07, Matthew Garrett <mjg59@...f.ucam.org> wrote:
> > On Sun, May 27, 2007 at 10:31:53PM +0200, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rjw@...k.pl>
> > >
> > > Use a hibernation and suspend notifier to disable the firmware requesting
> > > mechanism before a hibernation/suspend and enable it after the operation.
> >
> > This avoids the problem of .resume methods calling userspace while
> > userspace is frozen and a resulting hang, but does it actually result in
> > the drivers beginning to work again? If we remove process freezing in
> > STR, this should just work[1] without the need to complicate things. On
> > the other hand, if we don't want to support these functions in the
> > suspend and resume methods we could just audit the kernel and remove
> > them all.
> 
> What exactly is the problem we see here? The timeout of the firmware loader?
> What goes wrong with frozen userspace, usually there is only a netlink
> message sent from the kernel, which should be received and handled
> just fine when userspace is running again.

Users report the timeout as a problem and it's not that straightforward to
figure out what happens.

Still, I agree it's much better if drivers don't use request_firmware() in
their .resume() routines at all, because they shouldn't rely upon user land at
this point.

Greetings,
Rafael
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