linux-kernel - Re: what determines how firmware is loaded? (Q. on request

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Message-ID: <20120423212144.GA3378@kroah.com>
Date:	Mon, 23 Apr 2012 14:21:44 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	George Nychis <gnychis@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: what determines how firmware is loaded? (Q. on request_firmware
 details)

On Mon, Apr 23, 2012 at 04:18:56PM -0400, George Nychis wrote:
> Hi all,
> 
> I notice in an older version of Ubuntu that when I plugin a USB
> wireless device its firmware is loaded via sysfs.  For example, this
> would pop up in sysfs:
> /sys/devices/pci0000:00/0000:00:1d.7/usb2/2-1/compat_firmware/2-1/loading

How old are we talking about here?  What version of the kernel?

> In newer versions, I'm now seeing that the firmware seems to be loaded
> directly via a Kernel thread that is spawned.  It checks for the
> firmware in some firmware directory (e.g., /lib/firmware) and loads it
> to the device.

Yes.

> I see in documentation that one method is referred to as asynchronous.
>  Is this the  former or latter?

Depends on the device.

> Has the former method of loading firmware been removed as the default?
>  Is there any way to request that the firmware load be done manually
> (the former method)?

Why?  In the end, they do the same thing, right?

> It seems as though instead of calling request_firmware(), I could call
> _request_firmware() with "uevent" set to 0?  This would force for
> former behavior?
> 
> Does "nowait" also have to be 0?  I don't quite understand the
> separation between uevent and nowait.

I don't understand the problem here, isn't the end-result the same?
What is wrong with newer kernels?

thanks,

greg k-h
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