linux-kernel - Re: [PATCH] mfd: Combine MFD_SUPPORT and MFD

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Date:	Fri, 2 Sep 2011 14:37:13 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Luciano Coelho <coelho@...com>,
	Randy Dunlap <rdunlap@...otime.net>,
	matti.j.aaltonen@...ia.com, johannes@...solutions.net,
	linux-kernel@...r.kernel.org, sameo@...ux.intel.com,
	mchehab@...radead.org, linux-media@...r.kernel.org,
	linux-omap@...r.kernel.org, Tony Lindgren <tony@...mide.com>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH] mfd: Combine MFD_SUPPORT and MFD_CORE

Hi Arnd,

On Wed, 31 Aug 2011 18:49:37 +0200, Arnd Bergmann wrote:
> On Monday 29 August 2011, Luciano Coelho wrote:
> > From: Randy Dunlap <rdunlap@...otime.net>
> > 
> > Combine MFD_SUPPORT (which only enabled the remainder of the MFD
> > menu) and MFD_CORE.  This allows other drivers to select MFD_CORE
> > without needing to also select MFD_SUPPORT, which fixes some
> > kconfig unmet dependency warnings.  Modeled after I2C kconfig.
> > 
> > [Forward-ported to 3.1-rc4.  This fixes a warning when some drivers,
> > such as RADIO_WL1273, are selected, but MFD_SUPPORT is not. -- Luca]
> > 
> > Signed-off-by: Randy Dunlap <rdunlap@...otime.net>
> > Reported-by: Johannes Berg <johannes@...solutions.net>
> > Cc: Jean Delvare <khali@...ux-fr.org>
> > Cc: Tony Lindgren <tony@...mide.com>
> > Cc: Grant Likely <grant.likely@...retlab.ca>
> > Signed-off-by: Luciano Coelho <coelho@...com>
> > ---
> > 
> > I guess this should fix the problem.  I've simple forward-ported
> > Randy's patch to the latest mainline kernel.  I don't know via which
> > tree this should go in, though.
> > 
> > NOTE: I have not tested this very thoroughly.  But at least
> > omap2plus stuff seems to work okay with this change.  MFD_SUPPORT is
> > also selected by a couple of "tile" platforms defconfigs, but I guess
> > the Kconfig system should take care of it.
> 
> Doing this is a good idea, but incidentally I have just spent some time
> with the same problem and ended up with a solution that I like better,
> which is removing CONFIG_MFD_SUPPORT altogether.
> 
> The point is that there is no use enabling MFD_CORE if you don't also
> enable any of the specific drivers.

Same holds for pretty much every subsystem, right?

> MFD_SUPPORT was added as a 'menuconfig'
> before we had Kconfig warn about broken dependencies, so everything was
> fine. Since Kconfig now issues the warnings, I think it would be better
> to just turn the MFD menu into a plain 'menu' and remove all the
> 'depends on MFD_SUPPORT' and 'select MFD_SUPPORT' lines from the other
> Kconfig files.

This would make it impossible to turn off all MFD drivers at once. I
think this is considered a feature, at least I find it very convenient
to be able to "kill" a subsystem completely. And in the past few years
many subsystems were turned from menu to menuconfig for this reason.
But maybe MFD is a special case here.

Anyway, if you want your patch to be applied, you'll have to send it
for review first, as at this point all we have is Luciano's proposal.

-- 
Jean Delvare
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