linux-kernel - Re: loading firmware while usermodehelper disabled.

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Message-ID: <20111231201538.GA29758@srcf.ucam.org>
Date:	Sat, 31 Dec 2011 20:15:39 +0000
From:	Matthew Garrett <mjg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	drahemmaps@....net, davej@...hat.com, linux-kernel@...r.kernel.org,
	gregkh@...e.de, linux-usb@...r.kernel.org
Subject: Re: loading firmware while usermodehelper disabled.

On Sat, Dec 31, 2011 at 11:29:56AM -0800, Linus Torvalds wrote:

> But what the driver *should* be doing is to load the firmware at
> device open time (NOT at "driver load time" - because that can and
> does happen too early too, for the case of built-in drivers!) and
> simply keep the firmware around in the case of a suspend/resume event,
> so that it doesn't have to re-load it off a disk (or network, or
> whatever) that hasn't been resumed yet!

That doesn't work for the isight firmware loader - there's nothing for 
userspace to open until the device has had the firmware loaded, at which 
point it detaches and reattaches as a UVC device. The code could be 
merged into the UVC driver and a fake v4l device exposed, but even then 
you'd still need to deal with the underlying usb_device suddenly 
changing under you.

So for this specific case, I'd like to track down why the behaviour has 
changed - if the device was previously maintaining state over suspend 
and now isn't then that's something that's broken, but if it's just that 
some ordering has changed and now it's losing a race, I'll need to fix 
it in the driver. One option would be to do away with the kernelspace 
loader entirely and push it out to a udev helper, or alternatively just 
have the driver stash the firmware all the time.

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