linux-kernel - Re: [PATCH 2/3] ARM: ux500: Turn on the 'heartbeat' LED trigger

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Message-ID: <20130109122323.GE31678@gmail.com>
Date:	Wed, 9 Jan 2013 12:23:23 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Arnd Bergmann <arnd@...db.de>, sameo@...ux.intel.com,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linus.walleij@...ricsson.com
Subject: Re: [PATCH 2/3] ARM: ux500: Turn on the 'heartbeat' LED trigger

On Wed, 09 Jan 2013, Russell King - ARM Linux wrote:

> On Wed, Jan 09, 2013 at 11:08:40AM +0000, Lee Jones wrote:
> > On Wed, 09 Jan 2013, Russell King - ARM Linux wrote:
> > 
> > > On Wed, Jan 09, 2013 at 10:18:54AM +0000, Arnd Bergmann wrote:
> > > > On Wednesday 09 January 2013, Lee Jones wrote:
> > > > > diff --git a/arch/arm/mach-ux500/Kconfig b/arch/arm/mach-ux500/Kconfig
> > > > > index 5dea906..0f25b07 100644
> > > > > --- a/arch/arm/mach-ux500/Kconfig
> > > > > +++ b/arch/arm/mach-ux500/Kconfig
> > > > > @@ -43,6 +43,8 @@ config MACH_HREFV60
> > > > >  config MACH_SNOWBALL
> > > > >         bool "U8500 Snowball platform"
> > > > >         select MACH_MOP500
> > > > > +       select LEDS_TRIGGERS
> > > > > +       select LEDS_TRIGGER_HEARTBEAT
> > > > >         help
> > > > >           Include support for the snowball development platform.
> > > > 
> > > > Be careful with "select" statements like this when there are other
> > > > dependencies. I think LEDS_TRIGGERS depends on LEDS_CLASS, so this
> > > > should probably be written as
> > > > 
> > > > 	select LEDS_TRIGGERS if LEDS_CLASS
> > > 
> > > Umm, this is also wrong for another reason.  LEDS is an optional feature.
> > > It's not required for the platform to be functional.  So why the hell would
> > > anyone want to _force_ such an optional feature to be mandatory?
> > > 
> > > This is something that the default config published for the platform should
> > > be handling.
> > 
> > Do you mean <config_dir>/u8500_defconfig?
> > 
> > If so, that's wrong, as it covers many more boards than just Snowball
> > and this is only applicable on the Snowball board. So how else can
> > I enable this feature?
> 
> And why is it wrong to enable an optional feature in a defconfig which some
> boards using that defconfig may want?
> 
> It's _less_ wrong than forcing user selectable options to be mandatorily
> selected.

Excuse my ignorance, but I'm a little confused by this.

What's the difference between 'select <OPTION>' in the Kconfig and
'CONFIG_<OPTION>=y' in the defconfig; besides the fact that if we
do it in the Kconfig file, we can be more selective with regards to
which platform it gets enabled on?

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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