linux-kernel - Re: [RFC v1 01/16] lib: devres: don't enclose pcim_*() functions in CONFIG_HAS

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Message-ID: <20121211173819.6f2cf32b@skate>
Date:	Tue, 11 Dec 2012 17:38:19 +0100
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Arnd Bergmann <arnd@...db.de>, Lior Amsalem <alior@...vell.com>,
	Andrew Lunn <andrew@...n.ch>,
	Yehuda Yitschak <yehuday@...vell.com>,
	Maen Suleiman <maen@...vell.com>,
	Jason Cooper <jason@...edaemon.net>,
	Tawfik Bayouk <tawfik@...vell.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	linux-kernel@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Eran Ben-Avi <benavi@...vell.com>,
	Nadav Haklai <nadavh@...vell.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Shadi Ammouri <shadi@...vell.com>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Yinghai Lu <yinghai@...nel.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC v1 01/16] lib: devres: don't enclose pcim_*() functions in
 CONFIG_HAS_IOPORT

Russell,

On Tue, 11 Dec 2012 16:23:25 +0000, Russell King - ARM Linux wrote:

> > * ARCH_VEXPRESS should not select NO_IOPORT. It's generally wrong
> >   to select this in combination with ARCH_MULTIPLATFORM, when some
> >   of the other platforms you may enable actually have IOPORT mapping
> >   support.
> 
> No.  ARCH_VEXPRESS selects NO_IOPORT because it _does_ _not_ support
> PCI/ISA IO space.  That in itself is reasonable, but what isn't
> reasonable is the _negative_ logic being used.  Negative logic in
> the config system always tends to provoke this kind of sillyness
> because you're selecting something to be excluded which another
> platform may require.

Could you enlighten my very naive understanding of things about PCI/ISA
IO space? On x86, I seem to understand this is the separate address
space accessed by the special in/out CPU instructions. Are there ARM
platforms with the same sort of things?

As far as I understand, on my ARM Marvell system, everything is
memory-mapped, so there isn't such a separate PCI/ISA IO space.

Therefore, why would I need to "select HAVE_IOPORT" simply to be able
to build libata-sff.c, that is used for PCI drivers that work fine with
purely memory-mapped registers?

Sorry for the stupid/naive questions, but it'll definitely help to
understand the matter.

Thanks,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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