linux-kernel - Re: [PATCH 1/3] spi: Add a spi

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Date:	Fri, 27 Sep 2013 20:22:33 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Jean Delvare <khali@...ux-fr.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Jonathan Cameron <jic23@...nel.org>, lm-sensors@...sensors.org,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	linux-spi@...r.kernel.org
Subject: Re: [PATCH 1/3] spi: Add a spi_w8r16be() helper

On Fri, Sep 27, 2013 at 08:46:56PM +0200, Lars-Peter Clausen wrote:

> According to the documentation of spi_w8r16() it is a feature.

> 	* The number is returned in wire-order, which is at least sometimes
>  	* big-endian.

Indeed.  I don't think that's terribly well thought through though,
especially not now we have annotations for endianness (as you noticed!).

> There seem to be at least two users though which assume that the result is
> in native endianness drivers/hwmon/ads7871.c and drivers/mfd/stmpe-spi.c

Yeah, I saw.  The ads7871 is just going to break when run on the
opposite endianness to the one it was (hopefully) tested on since it
doesn't make any effort I saw to cope with endianness.  Looking at the
history it's not terribly obvious which that was but it'd be surprising
to see a little endian register...

STMPE is doing a byte swap so it's another user for your function -
it's for ARM systems so it'll be assuming that little endian is the
native format.

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