linux-kernel - Re: [PATCH 01/11] Add generic fixmap.h

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Date:	Tue, 12 Nov 2013 14:46:40 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Mark Salter <msalter@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org,
	Richard Kuo <rkuo@...eaurora.org>,
	linux-hexagon@...r.kernel.org,
	James Hogan <james.hogan@...tec.com>,
	linux-metag@...r.kernel.org, Michal Simek <monstr@...str.eu>,
	microblaze-uclinux@...e.uq.edu.au,
	Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...ux-mips.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 01/11] Add generic fixmap.h

On Tuesday 12 November 2013, Mark Salter wrote:
> Many architectures provide an asm/fixmap.h which defines support for
> compile-time 'special' virtual mappings which need to be made before
> paging_init() has run. This suport is also used for early ioremap
> on x86. Much of this support is identical across the architectures.
> This patch consolidates all of the common bits into asm-generic/fixmap.h
> which is intended to be included from arch/*/include/asm/fixmap.h.


Good idea, 

Acked-by: Arnd Bergmann <arnd@...db.de>

On Tuesday 12 November 2013, Mark Salter wrote:
> +static __always_inline unsigned long fix_to_virt(const unsigned int idx)
> +{
> +       /*
> +        * this branch gets completely eliminated after inlining,
> +        * except when someone tries to use fixaddr indices in an
> +        * illegal way. (such as mixing up address types or using
> +        * out-of-range indices).
> +        *
> +        * If it doesn't get removed, the linker will complain
> +        * loudly with a reasonably clear error message..
> +        */
> +       if (idx >= __end_of_fixed_addresses)
> +               __this_fixmap_does_not_exist();
> +

You might be able to turn this into the more readable BUILD_BUG_ON().

	Arnd
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