Message-ID: <266058be-3880-41ef-aa72-abc9377cec86@email.android.com>
Date:	Fri, 25 May 2012 17:21:54 +0100
From:	Jonathan Cameron <jic23@....ac.uk>
To:	Darren Hart <dvhart@...ux.intel.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"lkml, " <linux-kernel@...r.kernel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Éric Piel <eric.piel@...mplin-utc.net>,
	Carmine Iascone <carmine.iascone@...com>,
	Matteo Dameno <matteo.dameno@...com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: LIS331DLH accelerometer driver, IIO or not?





Darren Hart <dvhart@...ux.intel.com> wrote:

>
>
>On 05/25/2012 12:45 AM, Jonathan Cameron wrote:
>> Added Dmitry to the cc to get input on input side of things.
>>> On Thu, May 24, 2012 at 09:29:53PM -0700, Darren Hart wrote:
>>>> 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.
>>>
>>> Make it an IIO driver and then we can delete the misc driver, which
>>> shouldn't have snuck in there in the first place :)
>> Agreed. That would be what I'd suggest long term,
>
>Sure, but you're biased ;-)
>
>Joking aside, you and Greg made my day. I was afraid I had wasted
>several days grokking the 2.6.34 to 3.2 IIO subsystem changes!
>
> particularly when you
>> refer to 'bizarre and interesting'.  There are however some missing 
>> elements.  Note that none of these should stop you writing an iio
>> driver particularly as the current one doesn't support your part.
>> If you fancy pulling my lis3l02dq driver in as well (not sure how
>> close it is though ;) then feel free!
>
>I think I am going to start with a very simple lis331dlh only driver
>which supports sysfs polling. I'm working on the interrupt and smbalert
>interface currently, but I need something very soon. It would be good
>to
>get the simple stuff right and in tree so it doesn't bitrot as I work
>on
>the rest. Although, with the IIO core now in-tree and out of staging,
>hopefully things have settled down some?

Some... quite a lot of stuff still to do.  Will probably start keeping a 'what changed and how to follow' document though... userspace interfaces are pretty static. In kernel ones much less so!
>
>> 
>> lis3lv02d driver provides (I'm sure people are more familiar with
>this
>> than me, but it's helpful to lay it out).
>> 
>> /dev/freefall
>> joystick emulation through input. (looks like polled only? - guessing
>
>> the rates for interrupt driven were too high for general use)
>> Some x, y and z button inputs?
>> A couple of sysfs attributes we'd probably have to support in
>parallel
>> to new ones for compatability reasons (for a few kernel cycles
>anyway).
>> 
>> The one bit that doesn't map well at the moment is the click stuff.
>> I've been trying to avoid special purpose events like that by mapping
>> everything to the underlying real motion (these might be rate of
>> change of acceleration thresholds, but I doubt we'll find that in the
>> data sheets!) 
>
>The data sheets are rather sparse. I'm not sure what you mean by "rate
>of change of acceleration thresholds", but as the thresholds for this
>device are per-interrupt 
Pretty common
>(not axis nor direction) and only 6 bits
>(while
>the axis values are s16... I'm not sure what they are, and the
>datasheet
>makes no attempt to clarify the issue.

Hmm. 


>
>> Also right now we have no in kernel interface for
>> getting events - will require an extra layer and a demuxer similar
>> (but simpler) to the buffer one. Note as well that the buffer based
>> in kernel stuff is still under review (I'll try and get a rebased 
>> version out tomorrow).
>> 
>> So what are your bizarre and interesting then? (feel free not
>> to answer, but comments like that make me curious ;)
>
>Intel gave away vouchers for FRI2 devices to several attendees to the
>2012 ELC conference this year. We asked participants to do something
>cool and interesting with the device. I'm hoping some of them are more
>creative than I am! So the answer to your question is "I don't know",
>which is why I want to make it as configurable as possible to enable
>others to be bizarre and interesting :-)
>
>> Also any links to info on the fish river island II?
>> Google is failing me and I'm curious ;)
>
>Of course:
>http://us.kontron.com/products/systems+and+platforms/m2m/m2m+smart+services+developer+kit.html

Not sure how I failed to notice the link above!
>
>I'm developing the board support package for the Yocto Project for this
>device.
>
>http://www.yoctoproject.org/
>
>> 
>> Also, I'd almost have been inclinded to say this device should go
>> in input, with a few 'additional' interfaces, but sounds like you
>> want stuff input can't provide?
>
>I think bizarre and interesting things could certainly be done with the
>input system, but I'd prefer to expose the lower level features of the
>chip and not dictate how the chip is used. As you say, an input wrapper
>could be provided.
>
>One of the things I'm struggling with right now are having two
>interrupt
>lines. This device wires one to SMBALERT# and the other to a GPIO chip.
>I suppose this should be addressed using a custom platform_data struct

Yup.
>which I haven't implemented yet. My experimental i2c bus platform init
>code doesn't seem to work as expected... still working on that.
>
>While I have you Jon, I've run into an issue with the iio_chan_spec
>sysfs interface. I mark the modified bit and set IIO_MOD_X in channel2
>per the iio_chan_spec comments. But, iio_device_add_event_sysfs()
>ignores channel2 if chan->modified, so my event_code demuxer can't find
>the modifer and can't determine which axis I'm reading or writing event
>config for. I'm currently setting channel to IIO_MOD_X (or Y or Z) as a
>workaround, but I think I'm missing something.

Gah sounds like a bug snuck in. Just had a look. That is clearly wrong!  Feel free to send patch or I will get it tomorrow.  Thanks.

>
>The code is a bit of a mess right now as it is the result of my slowly
>rewriting it from a 2.6.34 version for 3.2 and fixing and enhancing as
>I
>go. I will try to clean it up and get it out for an RFC soon as this is
>my first real driver, I'm sure your input would be helpful.

Looking forward to it.
>
>-- 
>Darren Hart
>Intel Open Source Technology Center
>Yocto Project - Linux Kernel

-- 
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