linux-kernel - Re: __LITTLE_ENDIAN vs. __LITTLE_ENDIAN

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Message-ID: <470BC0D5.70305@freescale.com>
Date:	Tue, 09 Oct 2007 12:56:37 -0500
From:	Timur Tabi <timur@...escale.com>
To:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
CC:	Anton Altaparmakov <aia21@....ac.uk>,
	Jan Engelhardt <jengelh@...putergmbh.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: __LITTLE_ENDIAN vs. __LITTLE_ENDIAN_BITFIELD

Lennart Sorensen wrote:

>> You're talking about byte endian.  I'm talking about bit endian -- the 
>> order of bits within a byte.  Software cannot know what the bit endian is, 
>> but external devices that have memory-mapped registers can know.
> 
> The guy wiring up the hardware should connect the wires correctly.

I'm sure they're correct, my problem is that how can my driver know what they are?

> Doesn't the bus usually have some definition of bit order which the
> device would have to adhere to?  After all there must be address lines
> somewhere.

I was hoping that there would be some compile-time constant I could check that 
would give me this information.

> Does this perhaps offer anything useful?
> http://www.linuxjournal.com/article/6788

Yeah, I read that article some time ago when trying to diagnose the problem I 
was seeing.  It does explain the point I'm trying to make.  We have a device 
that's used on two product lines: one ARM-based, and one PowerPC.  The ARM is 
little-endian, and the PowerPC is big-endian.  The device can support 
little-endian or big-endian data, as long as the bit-order matches the byte-order.

For now, I'm going to have to assume that they do match.

-- 
Timur Tabi
Linux Kernel Developer @ Freescale
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