linux-kernel - Re: Do cpu-endian MMIO accessors exist?

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Message-Id: <200907221544.41054.arnd@arndb.de>
Date:	Wed, 22 Jul 2009 15:44:40 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Jiri Slaby <jirislaby@...il.com>, Pekka Paalanen <pq@....fi>,
	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>, lethal@...ux-sh.org,
	linux-sh@...r.kernel.org
Subject: Re: Do cpu-endian MMIO accessors exist?

On Wednesday 22 July 2009, Alan Cox wrote:
> 
> > in this case. Also, ioread32 should actually multiplex between
> > readl() and inl() based on the address token, as the code in
> > lib/iomap.c does. It's probably easy enough to enable
> > CONFIG_GENERIC_IOMAP on sh, and remove the ioread*/iowrite*
> > macros from arch/sh/include/asm/io.h.
> 
> If your platform is purely MMIO based then ioread32 and readl can become
> the same thing, which is much more efficient. Even if you have port based
> devices that are mapped as MMIO surely its more efficient to do the
> relevant address tweaking in the iomap not in the read ?

I did check that the architecture in question (sh) cannot do this,
because it actually implements board specific PIO functions in
arch/sh/boards/mach-*/io.c.

For architectures that don't need such hacks, I fully agree.

	Arnd <><
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