Re: User-space API for accelerometer(s)?

[Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>]

On 06/21/2014 05:37 AM, Bastien Nocera wrote:
> On Sat, 2014-06-21 at 13:01 +0100, Jonathan Cameron wrote:
>> On 19/06/14 12:20, Bastien Nocera wrote:
>>> On Wed, 2014-06-18 at 16:45 -0700, Srinivas Pandruvada wrote:
>>>> On 06/18/2014 04:31 PM, Reyad Attiyat wrote:
>>>>> Hello Bastien Nocera,
>>>>>
>>>>> I'm not the best person to answer your questions but I will try and
>>>>> help. The best people to talk to would be Jonathan Cameron, the IIO
>>>>> maintainer, and Srinivas Pandruvada, the author of the hid-sensor-hub
>>>>> device drivers. I have CC'ed them for you to hopefully get a better
>>>>> response than what I can offer.
>>>>>
>>>>> Your device uses the same sensor hub, over usb, as my device does. I
>>>>> have a Microsoft Surface and it also uses many of the sensors found on
>>>>> the Lenovo Yoga.
>>>>>
>>>>>> So, my question regarding the IIO user-space API is:
>>>>>> is it possible to make the IIO accelerometer send out a kevent when the
>>>>>> orientation changes in a major way (using triggers?) or does user-space
>>>>>> need to poll the device instead?
>>>> You can check a program called generic_buffer.c in
>>>> "drivers/staging/iio/Documentation". I have used this as a reference to
>>>> port to Android.
>>>> You don't need to poll, you can also check
>>>> "https://github.com/pfps/yoga-laptop/sensors " developed by Peter F.
>>>> Patel-Schneider.
>>> I've read this code, and in fact, I mentioned it in my original mail. I
>>> fail to see how this code isn't polling. It's also much more complicated
>>> than doing the same thing for a evdev accelerometer.
>>>
>> Just to throw it in there.  There is an out of tree bridge driver from
>> IIO to input.  It's only out of tree because I haven't had a chance to
>> tidy it up (anyone else is welcome to take this on if they like!)
>> Google for iio_input.c to find it.
> Found it, thanks :)
>
> http://thread.gmane.org/gmane.linux.kernel.iio/4464/
>
> (By the way, "iio_input", not "iio_snoop")
>
>> The intent of that was to allow general accelerometer drivers and similar
>> in IIO to work in conjunction with iio-input to provide input style interfaces.
>> This came about after previous debates on where the 'right' place for
>> accelerometers was in the kernel. I believe that at least in principle,
>> Dmitry was happy with this concept.
> Cool. The only question left would be whether this could throw a kevent
> when the orientation changes in a major way. This is a firmware feature
> in the WeTab/Pegatron machine, and is useful because it avoids the need
> to have the accelerometer constantly opened when not needed (saving
> battery by avoiding wakeups).
That will happen with sensor hubs, You can set the hysteresis to not to get
awakened unless the change is significant.

Thanks,
Srinivas

> Would it be worth adding such a feature inside the iio-input driver? I
> would have preferred it if the hardware sent those events, but I'd be
> happy just the same if the driver did it. The backing IIO device is
> always opened and processing data, it seems, whether or not the backing
> input device is opened in user-space or not.
>
> Cheers
>
>