linux-kernel - Re: A workaround for request_firmware() stuck in module

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Date:	Wed, 05 Sep 2012 16:01:23 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Ming Lei <ming.lei@...onical.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Kay Sievers <kay@...y.org>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: A workaround for request_firmware() stuck in module_init

At Wed, 5 Sep 2012 14:03:04 +0100,
Alan Cox wrote:
> 
> > If the driver is built in kernel, the request_firmware in .probe() may
> > prolong kernel init, and it might be a problem. But looks it is not a
> > big deal since most of drivers are built as module.
> 
> Doing it by deferring the load also fixes that. The built in ones will
> defer their final probe until the firmware appears and all will be well.
> 
> If your rootfs needs firmware not in your initrd you already broke it and
> there is a certain level beyond which you just have to give up trying to
> save people from themselves.
> 
> It may actually make sense to push more of it into the core driver layer
> and take some of the ability to make mistakes away from driver authors.
> For the general case of "load firmware if we see one" there isn't really
> any reason we can't have a firmware_name entry in the probe table
> entries themselves. If that was present the core bus probe would kick a
> firmware load off and only when the firmware had loaded would it call
> ->probe with dev->firmware pointing at a refcounted firmware struct.
> 
> At that point it should be much faster to fix existing drivers and much
> harder for a random device driver to get it wrong. We can even add
> helpers which manage dev->firmware, and free the relevant objects when
> needed, plus doing automatic ref/deref on probe/remove so that for a
> typical driver the author only has to do
> 
> 	{PCI_blah , ... .firmware_name="wibble500.xcr", }
> 
> and all the loading, unloading, not loading twice happens by "magic" for
> the driver author.
> 
> Add a dev_discard_firmware() for drivers that do this and know they can
> then dump the file and all is good 8)

This sounds like an interesting idea.  I guess majority of drivers can
be covered by this scenario.  Of course, there are a few drivers that
need more complex handling (e.g. iwlwifi handles fallback fw loading),
but they can be implemented manually if needed anyway.


Takashi
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