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    SubjectRe: LIS331DLH accelerometer driver, IIO or not?

    On 05/26/2012 10:40 AM, Jonathan Cameron wrote:
    > On 05/26/2012 12:53 PM, Éric Piel wrote:
    >> On 25-05-12 07:10, Greg Kroah-Hartman wrote:
    >>> 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.
    >>>> 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 :)
    >> To be more fair to the misc driver, I wouldn't say it snucked in there,
    >> but more "it ended up there as the least worse place" ;-) Actually, the
    >> main problem is that there seemed to be no maintainer interested in
    >> taking care of accelerometer devices. Now that the IIO subsystem is out
    >> of staging, it might be a right place. That said, I don't know much
    >> about the user interface to IIO. I know that I liked the idea of having
    >> an joystick device created for an accelerometer because that allows to
    >> get many programs to access the device almost without any modifications.
    > I agree that this sort of device should have an input interface. Not
    > sure if a joystick is the right option, but that's more one for Dmitry
    > to comment on.
    >> I'd happy to help merge the lis3lv02d driver into IIO. IMHO, the main
    >> steps are:
    >> * make sure all the various buses are supported (e.g., I²C, SPI, and
    >> also "ACPI-HP")
    >> * ensure the various versions of the accelerometer are supported (there
    >> are 3 supported currently)
    >> * check that the driver is automatically loaded on HP laptops (via ACPI
    >> entry)
    >> * for each of the current interfaces decide if they should be ported or
    >> dropped (/dev/js*, /dev/freefall, sysfs...)
    >> What do you think Jonathan?
    > You've laid it out extremely clearly. Thanks, I agree with these steps,
    > though they may occur from a slightly different angle given Darren is
    > interested in a part that is not (I believe) currently supported by
    > your existing driver. Hence he may initially want to do a separate
    > driver with that (keeping in mind the aim of mergining in the existing
    > driver). I have an ancient driver for the lis3l02dq alone (in
    > iio from the start) that will also get eaten up by Daren's new driver
    > (and the ability to test on that part on spi).
    > staging/iio/accel/lis3l02dq*.c

    I think I should start with getting the lis331dlh support completed, if
    for no other reason than to keep the scope manageable as I write my
    first real driver. From that I would like to merge in Jonathan's IIO
    lis3l02dq driver to get the multi-chip support part right. Then we
    should look at expanding the scope of the interface and finally merging
    with misc/lis3102dq. I believe that should meet with everyone's suggestions.

    One thing I would like to understand better is what sort of interface
    does userspace current expect. Phone Gap, for example, provides a very
    high level interface to applications in m/s^2 for each axis. Is there
    some interface we should ensure all accelerometer driver's implement?

    I suspect a /dev/accel interface that reads out xyz values in ms/s^2
    would make sense. We would need to ensure that allows for polled as well
    as event driven. Thoughts?

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