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

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Date:	Wed, 5 Sep 2012 13:59:56 -0300
From:	Lucas De Marchi <lucas.de.marchi@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Ming Lei <ming.lei@...onical.com>, Takashi Iwai <tiwai@...e.de>,
	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

On Wed, Sep 5, 2012 at 10:03 AM, Alan Cox <alan@...rguk.ukuu.org.uk> 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)


It seems like a good plan. So drivers that call request_module()
inside init_module() can be easily converted to this new scheme.

For those drivers that load the firmware upon open() syscal can be
left as is, right?

Then we can write the rule in stone: *don't call request_firmware from
init_module, instead give the name of the firmware*. I even see
drivers whose only purpose is to load the firmware and change the PID
so it's handled by another module (like drivers/bluetooth/bcm203x.c)
to be simplified by some extent.


Lucas De Marchi
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