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

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Message-Id: <6BD5252F-96CD-49D9-86C7-18115294D913@cam.ac.uk>
Date:	Sun, 27 May 2007 21:45:35 +0100
From:	Michael-Luke Jones <mlj28@....ac.uk>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.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 27 May 2007, at 21:31, 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.
>
> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
>
>  drivers/base/firmware_class.c |   36 ++++++++++++++++++++++++++++++ 
> ++++++
>  1 file changed, 36 insertions(+)

I don't like this approach, as I feel that the firmware loading  
interface should be able to detect if a firmware load request is not  
being handled, due to absence of userspace / hotplug handler presence.

Other circumstances in which this can be a problem is during bootup  
when request_firmware() calls can be made before userspace is up and  
init has run (even in the presence of an initramfs).

(Slightly OT: A particularly nasty race is when an initramfs  
userspace is present, but firmware loading cannot occur because init  
has not run, so proc hasn't been mounted, so a hotplug event handler  
cannot be registered, despite the fact that the firmware is sitting  
on the ramdisk mounted correctly...)

In short, a more general solution would be preferred, and preferably  
one which allows firmware loading to *actually* occur once userspace  
has actually turned up and registered a handler :)

Michael-Luke Jones

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