linux-kernel - Re: [PATCH 0/3] drivers: expand usage of request_firmware

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Date:	Wed, 9 Jul 2014 01:52:44 +0200
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Takashi Iwai <tiwai@...e.de>,
	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	chunkeey@...glemail.com, leedom@...lsio.com, cocci@...teme.lip6.fr,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-wireless@...r.kernel.org, linux-firmware@...nel.org
Subject: Re: [PATCH 0/3] drivers: expand usage of request_firmware_direct()

On Tue, Jul 08, 2014 at 03:25:36PM -0700, Greg KH wrote:
> On Thu, Jun 26, 2014 at 06:18:05PM +0200, Takashi Iwai wrote:
> > At Tue, 24 Jun 2014 15:39:40 -0700,
> > Luis R. Rodriguez wrote:
> > > 
> > > From: "Luis R. Rodriguez" <mcgrof@...e.com>
> > > 
> > > Takashi added request_firmware_direct() via bba3a87e9 through v3.14-rc1
> > > which avoids the unnecessary delay introduced by using the udev firmware
> > > loader in case the first try failed when loading we know loading "firmware"
> > > is optional. The first use case was for microcode update but if drivers are
> > > using it for optional configuration updates, custom EEPROMs, and other
> > > junk other than firmware that should apply as well as good use cases,
> > > specially if the driver already had a first phase in which it loaded
> > > the first required firmware. While reviewing one driver I figured it'd
> > > be best to try to give formalizing a check with SmPL. This isn't perfect
> > > it had 1 false possitive drivers/fmc/fmc-fakedev.c on the entire kernel
> > > run but my hope is this can be extended a bit more to build more
> > > confidence, and then perhaps stuff it as a coccicheck.
> > > 
> > > I suppose this will not be required once and if we remove
> > > CONFIG_FW_LOADER_USER_HELPER. Is that ever going away for good? I know
> > > there was a recent attempt to remove the udev loader support but
> > > it was unclear if the special alternative helper support would be
> > > removed upstream from the kernel.
> > 
> > Actually a few weeks ago I sent a patch to make request_firmware()
> > with usermode helper explicitly to be used by some drivers (like
> > dell-rbu).  I hope Greg took it for 3.17.  Once when this patch is in,
> > distros can turn off the usermode helper fallback gracefully, so no
> > ugly timeout issue shouldn't happen.
> 
> That patch is now merged, so this series should not be needed anymore,
> right?

Now that it is merged, and another patch I posted which you also merged about
printing differences, the main difference between request_firmware() and
request_firmware_direct() for distributions that did not enable the fw
loader helper is just a printk. That's all. While the difference is minor
this series addresses a few drivers that we know have firmware that is
optional, so a printk is indeed not really needed as otherwise it can confuse
users in terms of expectations. The SmPL grammar for this series could
likely be expanded to cover other uses cases but obviously this is not
critical and at best best effort. For distributions that stay in the stone age
and do not disable the fw loader helper this will speed up boot for a few use
cases. This series still applies then.

Whether or not its required or optional for firmware to be loaded for a driver
is an example small difference in specifications that I expect drivers /
subsystems to be able to make, I suspect the differences might grow in the
future so I rather keep these requirements well annonated for now. Another
example difference I am looking into is whether or not firmware should be
digitally signed. While it may be questionable whether or not this is needed
for actual firmware that runs on microprocessors some subsystems might want to
use this to abandon other udev helpers which simply throw data over, one of
which I am looking into replacing is CRDA for the regulatory database. We
recently ran into some snags when the internal regdb is used and we use a
parser, having the ability to load it directly using request_firmware_direct()
with digital signature support as an option would enable us to simplify how the
redb is used/parsed on both embedded and non-embedded systems.

  Luis
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