Message-ID: <4FBF0AC1.6030406@linux.intel.com>
Date: Thu, 24 May 2012 21:29:53 -0700
From: Darren Hart <dvhart@linux.intel.com>
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To: "lkml, " <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jonathan Cameron <jic23@kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>,
        =?ISO-8859-1?Q?=C9ric_Piel?= <eric.piel@tremplin-utc.net>,
        Carmine Iascone <carmine.iascone@st.com>,
        Matteo Dameno <matteo.dameno@st.com>
Subject: LIS331DLH accelerometer driver, IIO or not?
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I'm working to enable the LIS331DLH accelerometer on the Fish River
Island II embedded atom development kit.

http://www.st.com/internet/analog/product/218132.jsp

http://us.kontron.com/products/systems+and+platforms/m2m/m2m+smart+services+developer+kit.html

This device is attached to an i2c bus implemented in a CPLD (complex
programmable logic device) integrated on the compute module. I found an
IIO driver for the device written for 2.6.34. I've rewritten most of the
driver to work with the 3.2 kernel's IIO subsystem (and had planned to
next port it all the way to git HEAD and push it upstream).

However, I've since stumbled across a couple of things which cloud the
issue for me.

First, Carmine Iascone submitted a driver (driver/misc, not iio) for the
LIS331DLH back in Nov 2010.

http://lkml.org/lkml/2010/11/9/369

It was suggested that this driver be merged with the existing lis3lv02d
driver which listed support for a similar chip in the header, LIS331DL,
but it also lists LIS331DLF as not supported. The current git HEAD still
does not list LIS331DLH, and there is not a compatible register map in
the header.

Second, I came across the following TI document for porting the
LIS331DLH driver for Android:

http://processors.wiki.ti.com/index.php/TI-Android-GingerBread-2.3.4-DevKit-2.1_PortingGuides

This references a lis331dlh.c driver which I do not find in Linus' git
repository nor in linux-next.

So there are 3 ways I can go about this, and I'd appreciate any
direction on which would be the most acceptable for merging upstream.

1) Continue with my IIO version. This subsystem seems well suited to the
accelerometer. The iio_chan_spec simplifies the task of exposing the
event capabilities of the device, which the drivers/misc/lis3lv02d
driver mostly glosses over. It only supports events on free-fall for
example, while with IIO it is straight forward to enable interrupts for
rising and/or falling thresholds for each axis independently.

2) Attempt to merge Carmine's drivers/misc/lis331dlh driver with the
existing lis3lv02d driver as suggested in the thread mentioned above.
This driver isn't as fully functional.

3) Try and dig up the lis331dlh driver referenced in the TI document and
work to get that upstream. Like option 2, this driver is not likely to
be as configurable as the IIO driver.

I am more interested in enabling people to do bizarre and interesting
things with the device, so I'm leaning toward continuing with my IIO
implementation.

Thanks!

-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel
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