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

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Date:	Wed, 9 Jan 2013 13:00:04 +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

> > 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?
> 
> Take this in Kconfig:
> 
> config FOO
> 	bool "FOO option"
> 	select BAR
> 
> config BAR
> 	bool "BAR option"
> 
> Now, irrespective of the default configuration file being used:
> - if you don't enable FOO, then you can enable _and_ _disable_ BAR according
>   to your needs.
> - if you enable FOO, then BAR will be _forcefully_ enabled and you can't
>   turn it off without first disabling FOO.
> 
> The default configuration file will specify the _default_ values for these
> options, but if FOO ends up being enabled, BAR will be forcefully enabled
> irrespective of what's in the configuration file.
> 
> With this instead:
> 
> config FOO
> 	bool "FOO option"
> 
> config BAR
> 	bool "BAR option"
> 
> Then, the two options are independent.  They can be enabled and disabled
> by the configuration completely independently.  However, their default
> values come from the default configuration file.  So, if the config file
> has:
> 
> CONFIG_FOO=y
> CONFIG_BAR=y
> 
> and you do a 'make oldconfig' then they will remain set.  If you use one
> of the configuration editing tools, you'll be presented with them already
> enabled, and you can turn them off independently.
> 
> So, putting this stuff in the default configuration file allows
> _non-mandatory_ options to be disabled should the user desire without the
> user having to edit the configuration files.
> 
> If a user has to edit the configuration files in order to configure the
> kernel as they desire, then the configuration system has failed - or we
> have failed to properly think out how to represent the allowable
> configurations.

Understood. Thanks for the explanation.

Linus, is it okay to put these in the defconfig instead?

If so, I'll fixup.

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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