linux-kernel - Re: [RFC][PATCH] kconfig: implement select with values

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Date:	Mon, 26 Jul 2010 16:47:01 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Michal Marek <mmarek@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	linux-kbuild@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Roman Zippel <zippel@...ux-m68k.org>,
	Francis Galiegue <fgaliegue@...il.com>,
	Jiri Kosina <jkosina@...e.cz>, Andi Kleen <ak@...ux.intel.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Nir Tzachar <nir.tzachar@...il.com>,
	Vadim Bendebury <vbendeb@...gle.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Cheng Renquan <crquan@...il.com>, Trevor Keith <tsrk@...k.net>,
	Josh Triplett <josh@...htriplett.org>
Subject: Re: [RFC][PATCH] kconfig: implement select with values

Hi Sam,

On Mon, Jul 26, 2010 at 4:17 PM, Sam Ravnborg <sam@...nborg.org> wrote:
> On Tue, Jul 20, 2010 at 04:37:06AM +1000, Stephen Rothwell wrote:
>> This is a fairly brute force approach to allowing a Kconfig "select"
>> to specify an excplicit value for the selected config sybmol.
>>
>> The syntax of select is changed to:
>>
>>       "select" <symbol> [<expr>] ["if" expr]
>>
>> The approach taken is to add a list of <value, dependency expression>
>> pairs to the symbol and check them whenever the reverse depends (from
>> a current-style select) are checked.
>
> I do not see the need for this feature.
> I have read most of the postings in the defconfig battle and
> I saw Linus' select suggestion.
>
> But we can do almost all of this today (or tomorrow).
>
> Consider following Kconfig file:
>
>    config USB_SUPPORT
>            def_bool n
>
>    config NET
>            def_bool y
>
>    source arch/x86/Kconfig
>
> We use the feature that we can specify the same
> config option several times.
> And the first default value that is "visible"
> will be used.
>
> So it allows us to enable and disable any option.
>
> And if we for example want to set a specific LOG_BUF_SHIFT
> we use the same trick:
>
>    config LOG_BUF_SHIFT
>            int
>            default 14

Cute.  I didn't know this was possible.  I'll give it a try and see
how it works for me.  Do override config options also pickup
select/depends constraints applied by later definitions?  I think that
would be necessary to kick out warnings when a defconfig selection
isn't actually achievable.

g.

>
>
> Now in the original suggestion of Linus he used:
>
>    KBUILD_KCONFIG=Mykconfig make allnoconfig
>
> And "allnoconfig" would make the modified defaults useless.
>
> But the soon-to-be-introduced alldefconfig is more sensible.
>
> alldefconfig uses default values for everything.

I basically used defconfig in the prototype that I posted.  I think it
works well for me, and I've got it integrated into the build targets
(just like Stephen's earlier patch) without having to do a
KBUILD_KCONFIG trick.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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