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

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Date:	Tue, 3 Jan 2012 00:42:20 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jack Stone <jwjstone@...tmail.fm>
Cc:	Matthew Garrett <mjg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oliver@...kum.org>,
	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.

> Can we tell by the USB ids that this is a device that might need
> firmware and load it into memory anyway - it would use more memory but
> would always work as we would have the firmware.

Only by wasting a lot of memory in some cases. For the majority of cases
however yes you can take a good guess that id X might need firmware Y and
the firmware will only be a few K.

In that case however you don't want some generic firmware module knowing
all this crap, your driver can just request_firmware() the stuff as
modprobe and free it up on the module unload. For a typical 8bit firmware
of a few K you'll free a ton more memory unloading the module than the
firmware ! That I think actually covers the majority of devices under
discussion.

For the giant-firmware cases, it's unworkable on small devices - but they
are special cases anyway and almost entirely video - so not currently
ones that cause a problem unless you are doing RFC4824 in which case your
nearest asylum should be consulted.

Alan
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