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

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Date:   Fri, 10 May 2019 10:57:07 +0200
From:   Bastien Nocera <hadess@...ess.net>
To:     Roderick Colenbrander <thunderbird2k@...il.com>,
        Jonathan Cameron <jic23@...nel.org>
Cc:     "H. Nikolaus Schaller" <hns@...delico.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Eric Piel <eric.piel@...mplin-utc.net>,
        linux-input <linux-input@...r.kernel.org>,
        letux-kernel@...nphoenux.org, kernel@...a-handheld.com,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        lkml <linux-kernel@...r.kernel.org>, linux-iio@...r.kernel.org
Subject: Re: [RFC v2] iio: input-bridge: optionally bridge iio acceleometers
 to create a /dev/input interface

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?

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.