linux-kernel - Re: [PATCH] Kconfig: drop bogus default values

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Date:	Mon, 23 Mar 2015 22:08:24 +0100
From:	Martin Walch <walch.martin@....de>
To:	Paul Bolle <pebolle@...cali.nl>
Cc:	Jan Beulich <JBeulich@...e.com>, akpm@...ux-foundation.org,
	Michal Marek <mmarek@...e.cz>, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org, Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH] Kconfig: drop bogus default values

On Thursday 12 March 2015 13:11:47 Paul Bolle wrote:
> On Wed, 2015-03-11 at 13:59 +0000, Jan Beulich wrote:
> > Default "no" is pretty pointless for options without (visible) prompts:
> 
> Related: is there ever a situation where using "default n" or "def_bool
> n" makes sense (whether or not the entry has a prompt)? I think I once
> thought of one but I can't remember it at all, so I guess my memory is
> fooling me.

Your memory is right. It is rarely used, but there is an application for
using a plain "default n": to overwrite an existing other default value.
Particularly in one special case this is desired: Let us say there is a
symbol that may lack a visible prompt, but has the default value y set in
a Kconfig file that is used across all architectures. If there is a single
architecture that must have the default value n then it is possible to
override the default y in the global file with a default n in the
architecture specific file.

A real world case is PCI_QUIRKS in the mainline kernel:

init/Kconfig:1554:	default y
arch/s390/Kconfig:59:	def_bool n

When setting PCI!=n && EXPERT=n then on each architecture PCI_QUIRKS=y
except on s390 where PCI_QUIRKS=n.

Regards,
Martin Walch
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