linux-kernel - Re: will these methods work with firmware loading?

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Message-ID: <4F421A0E.8030805@broadcom.com>
Date:	Mon, 20 Feb 2012 11:01:50 +0100
From:	"Arend van Spriel" <arend@...adcom.com>
To:	"Larry Finger" <Larry.Finger@...inger.net>
cc:	LKML <linux-kernel@...r.kernel.org>,
	driverdevel <devel@...verdev.osuosl.org>,
	wireless <linux-wireless@...r.kernel.org>,
	"linux-hotplug@...r.kernel.org" <linux-hotplug@...r.kernel.org>,
	"Kay Sievers" <kay.sievers@...y.org>
Subject: Re: will these methods work with firmware loading?

On 02/19/2012 07:40 PM, Larry Finger wrote:
> I sent a previous messages to most of these lists, but got no answer, thus a
> second try.
>
> When a driver loads firmware synchronously in the module_init() path using
> request_firmware(), then there is trouble with timeouts when booting.
>
> I know that changing the request_firmware() call to request_firmware_nowait()
> solves the problem; however, that gives some trouble for driver b43legacy as it
> loads 3 or 4 firmware files depending on the hardware version. When I launch the
> 3 or 4 nowait requests, I get an error because the system is trying to start
> several tasks with the same name.

Yep, the nowait api just kicks off a kernel thread for the firmware request.

> Would it be OK to load the first file with the nowait version, and issue a
> request_firmware() for the others from the callback routine? I think that would
> not cause any problems, but I would like to get confirmation from an expert.

No expert, but that is what I did although the chaining of firmware 
requests does not feel great. Especially for handling error flows. 
Johannes Berg and Kay Sievers mentioned need to unbind/rebind the driver 
upon failed firmware load, but I don't like the idea of building a 
timer-controlled retry mechanism.

> Similarly, if I were to create a work queue, init and schedule it from
> module_init(), and then use synchronous loads to get the firmware from the work
> queue callback, would that get around the boot problem? I know it works as I
> have trial patches; however, my version of udev is not one affected. This method
> is very easy to implement, but again I would like confirmation from an expert.

What boot problem are you referring to? The blocking modprobe? For that 
problem I would say yes. Also here the problem of handling error flows 
exist. If the driver is kicked of during boot with a initramfs missing 
the firmware, should we retry until the real root is mounted?

Gr. AvS

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