linux-kernel - Re: [PATCH] ARM: Gemini: Add support for PCI Bus

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Message-ID: <20101130160527.GB2377@n2100.arm.linux.org.uk>
Date:	Tue, 30 Nov 2010 16:05:27 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Hans Ulli Kroll <ulli.kroll@...glemail.com>,
	linux-arm-kernel@...ts.infradead.org,
	Michał Mirosław <mirqus@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: Gemini: Add support for PCI Bus

On Mon, Nov 29, 2010 at 04:57:53PM +0100, Arnd Bergmann wrote:
> On Monday 29 November 2010, Hans Ulli Kroll wrote:
> > @@ -1164,7 +1169,7 @@ config ISA_DMA_API
> >         bool
> >  
> >  config PCI
> > -       bool "PCI support" if ARCH_INTEGRATOR_AP || ARCH_VERSATILE_PB || 
> > ARCH_IXP4XX || ARCH_KS8695 || MACH_ARMCORE || ARCH_CNS3XXX
> > +       bool "PCI support" if MIGHT_HAVE_PCI
> >         help
> >           Find out whether you have a PCI motherboard. PCI is the name of 
> > a
> >           bus system, i.e. the way the CPU talks to the other stuff inside
> 
> This does not solve the problem that Russell mentioned: existing platforms
> select PCI unconditionally, e.g. Iop13XX, some IXP, Orion, Shark
> and more. At the very least, these would need to also select MIGHT_HAVE_PCI
> to avoid the warning.

No, the above is correct.  What I was talking about was the difference
between these:

config PCI
	bool "PCI support" if MIGHT_HAVE_PCI

and

config PCI
	bool "PCI support"
	depends on MIGHT_HAVE_PCI

In the first instance, PCI itself does not depend on MIGHT_HAVE_PCI.
MIGHT_HAVE_PCI controls whether the user is offered the "PCI support"
option.

In the second instance, PCI depends on MIGHT_HAVE_PCI, which must be
set to 'y' to offer the option _and_ also if PCI is selected.

We want the first behaviour.  Platforms which must have PCI support can
continue to select PCI as they currently do, and leave the MIGHT_HAVE_PCI
option alone.

Platforms which may optionally have PCI support should select
MIGHT_HAVE_PCI instead.
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