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

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Message-Id: <5511227F020000780006CD25@mail.emea.novell.com>
Date:	Tue, 24 Mar 2015 07:38:23 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Paul Bolle" <pebolle@...cali.nl>,
	"Martin Walch" <walch.martin@....de>
Cc:	<akpm@...ux-foundation.org>, "Sam Ravnborg" <sam@...nborg.org>,
	"Michal Marek" <mmarek@...e.cz>, <linux-kbuild@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Kconfig: drop bogus default values

>>> On 23.03.15 at 22:08, <walch.martin@....de> wrote:
> 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.

But iirc such redundant defaults yield warnings (or at least at
some point in the past they did).

Jan

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