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Date: Tue, 3 Jun 2008 09:46:46 +0200
From: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
To: Scott Wood <scottwood@freescale.com>
Subject: Re: MMIO and gcc re-ordering issue
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Cc: linux-arch@vger.kernel.org, Matthew Wilcox <matthew@wil.cx>,
	linux-kernel@vger.kernel.org, tpiepho@freescale.com,
	linuxppc-dev@ozlabs.org, Geert Uytterhoeven <geert@linux-m68k.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	David Miller <davem@davemloft.net>, alan@lxorguk.ukuu.org.uk
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Scott Wood <scottwood@freescale.com> wrote:
> On Mon, Jun 02, 2008 at 10:11:02AM +0200, Haavard Skinnemoen wrote:
> > Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > On Fri, 30 May 2008, Haavard Skinnemoen wrote:
> > > > Maybe we need another interface that does not do byteswapping but
> > > > provides stronger ordering guarantees?
> > > 
> > > The byte swapping depends on the device/bus.
> > 
> > Of course. But isn't it reasonable to assume that a device integrated
> > on the same silicon as the CPU is connected to a somewhat sane bus
> > which doesn't require any byte swapping?
> 
> No, unfortunately. :-(

Ok, I guess I was being naive.

> See the end of drivers/dma/fsldma.h.  Likewise with Freescale's PCI host
> bridges; for some reason the bus itself being little endian led to the host
> bridge control registers also being little endian.

Right. But still, isn't it better to handle it on a case-by-case basis
in the drivers? In some cases, it's best to explicitly use a certain
byte order, in others it's best to use whatever is native to the CPU.

Haavard