linux-kernel - Re: [PATCH] drivers/block/xsysace - replace in(out)_8/in(out)_be16/in(out)

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Message-ID: <1360067383.4529.8.camel@pasglop>
Date:	Tue, 05 Feb 2013 23:29:43 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:	Michal Simek <monstr@...str.eu>, Arnd Bergmann <arnd@...db.de>,
	Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
	linux-kernel@...r.kernel.org, grant.likely@...retlab.ca,
	alan@...rguk.ukuu.org.uk, geert@...ux-m68k.org,
	dahinds@...rs.sourceforge.net, Noam Camus <noamc@...hip.com>
Subject: Re: [PATCH] drivers/block/xsysace - replace
 in(out)_8/in(out)_be16/in(out)_le16 with generic iowrite(read)8/16(be)

On Tue, 2013-02-05 at 17:39 +0530, Vineet Gupta wrote:
> Am I correct in understanding that "be" suffix here reflects the byte ordering of
> the device and not the CPU. So for a BE device, driver using ioread32be on LE
> processor will get MSB first data - and accessor will swap the bytes to make it
> lsb first in register, while on BE processor, the lanes to memory are swapped,
> causing the msb first word to be flipped before ending up in the cpu register - so
> in the end, CPU register on either will have the exact same value. Correct ?

Yes. That's how ioread32 and ioread32be are defined. They relate to the device
endianness regardless of the CPU endianness.

ioread32 -> little endian device
ioread32be -> big endian device

Cheers,
Ben.


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