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

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Message-ID: <4F0219AB.6010505@fastmail.fm>
Date:	Mon, 02 Jan 2012 20:55:07 +0000
From:	Jack Stone <jwjstone@...tmail.fm>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oliver@...kum.org>,
	Matthew Garrett <mjg@...hat.com>,
	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Larry Finger <Larry.Finger@...inger.net>,
	Chaoming Li <chaoming_li@...lsil.com.cn>,
	"John W. Linville" <linville@...driver.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	USB list <linux-usb@...r.kernel.org>,
	Linux Wireless List <linux-wireless@...r.kernel.org>
Subject: Re: loading firmware while usermodehelper disabled.

On 02/01/12 20:48, Linus Torvalds wrote:
> On Mon, Jan 2, 2012 at 12:41 PM, Jack Stone <jwjstone@...tmail.fm> wrote:
>>
>> What about the case where the firmware that needs to be loaded is on the
>> USB device that needs the firmware. This can be resolved at boot using
>> an initrd but at resume time we don't have that.
> 
> Quite frankly, caching the firmware will just automagically fix this.
> 
> I don't understand why people even bother to talk about USB ID's etc
> changing - that is totally irrelevant. We don't look up firmware by
> USB ID's anyway.

I agree. The only problem I can see is with the lifetime of the
firmware. If we have a generic USB driver that looks after (for example)
all USB disks then we do not want to add the knowedge to it for each
individual vendors firmware.

For example:

	1/ Plug in device, registers as a bootstrap device
	2/ Load firmware into device (and put firmware in cache)
	3/ Device disconnects and reconnects with new USB id
	4/ Generic driver takes over as it recognizes the new id

The problem comes with knowing when to put the firmware - how do we tell
the generic driver that that device has firmware that might need to be
freed on disconnect. I don't know enough about USB to know if we can
tell if the same device has reconnected due to firmware being loaded or
if it was simply unplugged and a new device plugged in.

Hope this makes sense,

Jack

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