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Date: Thu, 7 Feb 2013 20:56:33 +0400
From: Alexey Brodkin <Alexey.Brodkin@synopsys.com>
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To: Grant Likely <grant.likely@secretlab.ca>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Michal Simek <monstr@monstr.eu>, Arnd Bergmann <arnd@arndb.de>,
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>,
        "Geert Uytterhoeven" <geert@linux-m68k.org>,
        <dahinds@users.sourceforge.net>
Subject: Re: [PATCH] drivers/block/xsysace - replace in(out)_8/in(out)_be16/in(out)_le16
 with generic iowrite(read)8/16(be)
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On 02/07/2013 08:44 PM, Grant Likely wrote:
>
> Then that data needs to be stored into memory. This is where things
> are different with native 16 bit stores:
>    On a BE memory system. MSB in byte address 0 and LSB in byte address 1.
>    On a LE memory system. MSB in byte address 1 and LSB in byte address 0.
>
> The block subsystem deals with byte oriented buffers; so given the way
> data is arranged in the data port we want to always make sure the LSB
> goes into address 0. The cause of problems isn't the BE vs LE bus
> attachment. It is the different memory system orientation. Using
> ioread16/iowrite16 has the right behaviour, but it's kind of a
> backwards way to go about it.... It isn't that we want a be16_to_cpu()
> or le16_to_cpu() on the data port read, but rather a cpu_to_le16() on
> the store to memory regardless of the endianess of the platform.
>
> So, if I'm correct that means that for the data port (specifically
> copying between RAM and the data port) using ioread16/iowrite16 on the
> data port results in the correct behaviour. It also means that LE
> support in the current driver is broken.

That matches my earlier note when I wrote that for correct work on LE 
(note I'm on ARC, not PPC/MB) I needed to use "io{read|write}16" in 
"ace_data{in|out}_le16".

With original "io{read|write}16be" instead data was corrupted.

-Alexey