linux-kernel - Re: [PATCH 4/9] ARM: add CONFIG_PHYS

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Message-ID: <alpine.LFD.2.20.1602191215140.13632@knanqh.ubzr>
Date:	Fri, 19 Feb 2016 12:31:02 -0500 (EST)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
cc:	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Jon Medhurst <tixy@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/9] ARM: add CONFIG_PHYS_OFFSET default values

On Fri, 19 Feb 2016, Arnd Bergmann wrote:

> On Friday 19 February 2016 11:10:22 Nicolas Pitre wrote:
> > On Fri, 19 Feb 2016, Arnd Bergmann wrote:
> > 
> > > On Thursday 18 February 2016 11:02:33 Nicolas Pitre wrote:
> > > > 
> > > > Acked-by: Nicolas Pitre <nico@...aro.org>
> > > > 
> > > > Is there a way to provide a default for defaults?
> ...
> > > and then select one of the bool symbols from each platform.
> > > Would that address your question?
> > 
> > Yes, but the ugliness factor isn't worth it IMHO.
> > 
> > I was wondering if something like this was possible:
> > 
> > config PHYS_OFFSET
> >         hex "Physical address of main memory" if MMU
> >         default DRAM_BASE if !MMU
> >         default 0x10000000 if FOO
> >         default 0x20000000 if BAR
> >         default 0x30000000 if BAZ
> >         default 0x00000000
> > 
> 
> Ah, that was my previous approach, but Russell didn't like
> how it makes it easier to fall back to an incorrect address
> instead of forcing a build error when the address is not
> configured.

Makes sense.

Yet, the only reason for a default here is to accommodate automatic 
build tests like randconfig, right?

If so then this should be "fixed" by having the config system provide 
built-in symbols that can be tested from kconfig files.  This way you 
could terminate the above list with:

	default 0x00000000 if RANDCONFIG || ALLYESCONFIG

or the like.


Nicolas