linux-kernel - Re: [PATCH 4/5] kconfig: Introduce "showif" to factor out conditions on visibility

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Date:	Thu, 28 May 2015 16:57:40 +0200
From:	Paul Bolle <pebolle@...cali.nl>
To:	josh@...htriplett.org
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Michal Hocko <mhocko@...e.cz>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Andy Lutomirski <luto@...capital.net>,
	Bertrand Jacquin <beber@...eeweb.net>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Iulia Manda <iulia.manda21@...il.com>,
	Pranith Kumar <bobby.prani@...il.com>,
	Clark Williams <clark.williams@...il.com>,
	Mel Gorman <mgorman@...e.de>,
	Randy Dunlap <rdunlap@...radead.org>,
	Michal Marek <mmarek@...e.cz>, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] kconfig: Introduce "showif" to factor out
 conditions on visibility

On Wed, 2015-05-20 at 11:30 -0700, josh@...htriplett.org wrote:
> In net/rfkill/Kconfig, RFKILL_REGULATOR oddly has
> "depends on RFKILL || !RFKILL".  WIMAX does the same thing.

That's only tristate logic. It's a common idiom, but it looks very odd
compared to boolean logic. It ensures RFKILL_REGULATOR will not be 'y'
if RFKILL is 'm'. Because:
    RFKILL = 'n' => RFKILL_REGULATOR = 'n' || 'm' || 'y'
    RFKILL = 'm' => RFKILL_REGULATOR = 'n' || 'm'
    RFKILL = 'y' => RFKILL_REGULATOR = 'n' || 'm' || 'y'

Hope this helps,


Paul Bolle

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