linux-kernel - Re: [PATCH] ARM: supplementing IO accessors with 64 bit capability

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Message-ID: <20141022171942.GC27405@n2100.arm.linux.org.uk>
Date:	Wed, 22 Oct 2014 18:19:42 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	stefano.stabellini@...citrix.com,
	ezequiel.garcia@...e-electrons.com,
	Liviu Dudau <Liviu.Dudau@....com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: supplementing IO accessors with 64 bit capability

On Wed, Oct 22, 2014 at 06:22:09PM +0200, Mathieu Poirier wrote:
> I had this conversation with a colleague who reviewed the work.  If
> the architecture is < 5 the __raw_ versions aren't included and the
> compiler won't complain until someone tries to use the macros.  We
> achieve the same result - the macros aren't accessible when the
> architecture doesn't support it - while saving an #if condition in the
> file.
> 
> I'm not strongly opinionated on this - I can enclose the macros in an
> #if statement.

What you're missing is that some driver may test for their presence by
doing:

#ifndef readq_relaxed
... do something else

which would now break as a detection method, as the macro is always
defined no matter whether it's present or not.

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