linux-kernel - Re: [PATCH] firmware loader: allow disabling of udev as firmware loader

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Date:	Wed, 04 Jun 2014 16:31:47 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Tom Gundersen <teg@...m.no>
Cc:	linux-kernel@...r.kernel.org, Ming Lei <ming.lei@...onical.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Abhay Salunke <Abhay_Salunke@...l.com>,
	Stefan Roese <sr@...x.de>, Arnd Bergmann <arnd@...db.de>,
	Kay Sievers <kay@...y.org>
Subject: Re: [PATCH] firmware loader: allow disabling of udev as firmware loader

At Wed, 04 Jun 2014 16:20:16 +0200,
Takashi Iwai wrote:
> 
> At Mon,  2 Jun 2014 20:24:34 +0200,
> Tom Gundersen wrote:
> > 
> > Currently (at least) the dell-rbu driver selects FW_LOADER_USER_HELPER,
> > which means that distros can't really stop loading firmware through udev
> > without breaking other users (though some have).
> > 
> > Ideally we would remove/disable the udev firmware helper in both the kernel
> > and in udev, but if we were to disable it in udev and not the kernel, the result
> > would be (seemingly) hung kernels as no one would be around to cancel firmware
> > requests.
> > 
> > This patch allows udev firmware loading to be disabled while still allowing
> > non-udev firmware loading, as done by the dell-rbu driver, to continue
> > working. This is achieved by only using the fallback mechanism when the
> > uevent is suppressed.
> > 
> > Tested with
> >     FW_LOADER_USER_HELPER=n
> >     LATTICE_ECP3_CONFIG=y
> >     DELL_RBU=y
> > and udev without the firmware loading support, but I don't have the hardware
> > to test the lattice/dell drivers, so additional testing would be appreciated.
> 
> The logic of this patch looks good to me, but the Kconfig items become
> confusing by this.  Basically what we'd need is a Kconfig item
> deciding whether to build the user helper or not, in addition to a
> Kconfig item for deciding the fallback mode of request_firmware().
> 
> What about the patch like below instead?  It's smaller and the meaning
> of Kconfig items are clearer.  (In the final form, the help text
> change you added should be included there, too.)
> 
> The only (and biggest) drawback is, however, that the user-selectable
> Kconfig would be actually renamed from CONFIG_FW_LOADER_USER_HELPER to
> CONFIG_FW_LOADER_USER_HELPER_FALLBACK.

Also, since it's deprecated in the udev upstream, let's drop "default
y", too.  (It can be another patch, though.)


Takashi
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