linux-kernel - Re: [PATCH v12 05/11] edma: config: Enable config options for EDMA

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Message-Id: <201306211600.04986.arnd@arndb.de>
Date:	Fri, 21 Jun 2013 16:00:04 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Joel A Fernandes <agnel.joel@...il.com>
Cc:	Sekhar Nori <nsekhar@...com>, Joel A Fernandes <joelagnel@...com>,
	Tony Lindgren <tony@...mide.com>,
	Matt Porter <matt@...orter.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Benoit Cousson <b-cousson@...com>,
	Russell King <linux@....linux.org.uk>,
	Rob Landley <rob@...dley.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jason Kridner <jkridner@...gleboard.org>,
	Koen Kooi <koen@...gleboard.org>,
	Devicetree Discuss <devicetree-discuss@...ts.ozlabs.org>,
	Linux OMAP List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Documentation List <linux-doc@...r.kernel.org>,
	Linux MMC List <linux-mmc@...r.kernel.org>,
	Linux SPI Devel List 
	<spi-devel-general@...ts.sourceforge.net>
Subject: Re: [PATCH v12 05/11] edma: config: Enable config options for EDMA

On Friday 21 June 2013, Joel A Fernandes wrote:
> >> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> >> index b1c66a4..7d58cd9 100644
> >> --- a/arch/arm/Kconfig
> >> +++ b/arch/arm/Kconfig
> >> @@ -841,6 +841,7 @@ config ARCH_DAVINCI
> >>       select HAVE_IDE
> >>       select NEED_MACH_GPIO_H
> >>       select TI_PRIV_EDMA
> >> +     select DMADEVICES
> >
> > It is generally a bad idea to force select on something that can be
> > enabled using menuconfig. Unless used carefully, select causes "unmet
> > direct dependency" warnings which folks are already fighting hard to
> > fix. This leads to what Russell referred in the past as "select madness" [1]
> 
> Are you concerned with bloat issues? I know your point of view but the idea
> was to build these options by default for these platforms even though
> in some cases
> it might not be used. I have seen folks including myself select the wrong
> option. Having the build system automatically select the correct option for the
> most common cases can be very useful I feel and not require manual
> configuration.

For defaults, you should use the defconfig, not 'select' in Kconfig.

A lot of the 'select' statements are actually wrong because they
do not take dependencies into account where A selects B but not C,
and B depends on C, which leads to broken builds when C is disabled
by a user (or randconfig).

You should only ever use 'select' from platforms on silent options
that are not themselves user selectable like the above 'HAVE_IDE'
and 'NEED_MACH_GPIO_H'.

	Arnd
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