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

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Message-Id: <BDEF3C8A-D237-44C4-84E0-2218DFAE0E77@cam.ac.uk>
Date:	Mon, 28 May 2007 13:26:37 +0100
From:	Michael-Luke Jones <mlj28@....ac.uk>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Pavel Machek <pavel@....cz>, "Rafael J. Wysocki" <rjw@...k.pl>,
	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>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [RFC][PATCH -mm 3/3] PM: Disable _request_firmware before hibernation/suspend

On 28 May 2007, at 12:51, Kay Sievers wrote:

> Either the whole idea of userspace firmware-loading should be  
> considered
> as a problem impossible to do right because of its unsolvable side
> effects. Or at least releasing loaded firmware should be the exception
> for drivers which can be sure, that the firmware is not needed in
> situations we try to work around here.

I don't believe that it is impossible. What is needed is some  
thought, and maybe a loose spec.

We need to think about safe ways of solving a simple problem: what to  
do when userspace is unable to respond to a kernel uevent request. We  
now have a timeout, whether it be handled synchronously or in the  
background. I don't think either solution is good enough.

[RFC] Possible Plan:

1) request_firmware() should stick around unmodified but be marked  
__deprecated.

2) request_firmware_nowait() as it stands should probably be removed.  
After all, it only has 2 in-kernel users at the moment.

3) uevent interface should be notified when userspace handlers are /  
are not available so that events can be queued to be handled when  
userspace does turn up and re-register a hotplug event handler.

4) request_firmware_async() introduced: asynchronous firmware loading  
interface built on basis of 3, such that problems at early boot and  
suspend / resume are avoided. Also request_firmware_async() taught to  
retain firmware in memory by default such that subsequent calls do  
not require a call to userspace if userspace is unavailable.

6) Documentation on correct firmware loading behaviour for driver  
authors written, together with migration notes for existing users of  
request_firmware().

7) Existing uses of request_firmware() converted.

*Grumble ahead*
Unfortunately, I don't properly understand the uevent interface, so  
some of the above may be inaccurate. This is *not* my fault as there  
is no decent documentation (and btw, telling me to write the  
documentation is not the answer to that problem).

Michael-Luke
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