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

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Message-ID: <4F42A935.90603@lwfinger.net>
Date:	Mon, 20 Feb 2012 14:12:37 -0600
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Kay Sievers <kay.sievers@...y.org>
CC:	Arend van Spriel <arend@...adcom.com>,
	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>
Subject: Re: will these methods work with firmware loading?

On 02/20/2012 04:19 AM, Kay Sievers wrote:
> On Mon, Feb 20, 2012 at 11:01, Arend van Spriel<arend@...adcom.com>  wrote:
>> On 02/19/2012 07:40 PM, Larry Finger wrote:
>
>>> 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.
>
> It sounds like it should work, because the modprobe event returns, not
> waiting for the firmware request. Chaining one firmware request after
> the other sounds not like a problem, as long as they are chained with
> the return from the earlier request and not from inside the earlier
> request, which would have duplicated device name issues in the kernel
> too.
>
>> What boot problem are you referring to?
>
> The pci event calls modprobe, the module init for the pci driver
> creates a child event of the pci device, this child event is queued in
> udev to be started after the pci event has finished. The pci event
> does not finish in time because the firmware request blocks itself.
>
> The current udev logic limits the timeout to 30 sec, while the
> firmware request is 60 sec, so it usually works with a logged error,
> and a 30 second delay.
>
>> The blocking modprobe?
>
> Yes, blocking in the module init path, will deadlock udev. Linking
> code into the kernel must not depend on device init or firmware
> loading.
>
>> 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?
>
> I don't think so. Drivers are not supposed to know about bootup or
> initramfs issues. If they want, they can disable the timeout, and wait
> for userspace to handle the request any time later, but they should
> not try to be smart here.
>
> Currently, firmware requests are cancelled if the firmware isn't
> found, but that's a userspace issue, and nothing the kernel should try
> to work around.

Kay,

Thanks for your very helpful comments. I think I will keep my second method, 
i.e. start a work queue entry from the probe routine, and then use synchronous 
firmware loads from that queue's callback routine. In most cases, the firmware 
loading is already done from a separate routine, thus the flow is not that 
different from the current code.

Larry

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