[Letux-kernel] [RFC v2] iio: input-bridge: optionally bridge iio acceleometers to create a /dev/input interface

Roderick Colenbrander thunderbird2k at gmail.com
Sat May 11 20:47:30 CEST 2019

On Fri, May 10, 2019 at 1:57 AM Bastien Nocera <hadess at hadess.net> wrote:
> On Sun, 2019-04-14 at 09:26 -0700, Roderick Colenbrander wrote:
> >
> <snip>
> > We at the time were one of the first to expose acceleration and gyro
> > data through /dev/input for DualShock 4 as supported by hid-sony. We
> > report acceleration in 'g' and angular velocity in 'degree / s'. We
> > set the resolution to respectively '1 g' and '1 degree / s'. The range
> > we set to the range of the device e.g. for DS4 -4g to +4g for
> > acceleration. I need to check though what coordinate system we use,
> > but I think it is right handed (gyro counter clockwise relative to
> > acceleration axes).
> How do you export the gyro information through the input device?

For each DS4, there are multiple evdev devices for a DS4 for
respectively "gamepad", touchpad and motion sensors. The motion
sensors one, has INPUT_PROP_ACCELEROMETER set. ABS_X/_Y_Z provide
acceleration and ABS_RX/_RY/_RZ provide gyro. When we added this we
also updated the input documentation (event-codes.rst) to allow gyro
to use the rotational axes.

> FWIW, we needed to do extra work in iio-sensor-proxy so that the
> accelerometer in the Sixaxis/DS4 joypads (and uDraw tablet) didn't
> appear as though they were accelerometer for the system:
> https://github.com/hadess/iio-sensor-proxy/commit/401d59e54b3123860180d4401e09df8a1e1bc6c3
> > The two other drivers using INPUT_PROC_ACCELEROMETER are hid-wacom and
> > hid-udraw-ps3 Wacom. Both seem to report resolution in 'g'  as well.
> I wrote hid-udraw-ps3, and it's reporting accelerometer data through
> input because the rest of the driver is input, and it didn't make much
> sense to use another subsystem for just that small portion of the
> events the device sends out.

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