Re: Accelerometer, Gyros and ADC's etc within the kernel.

From: Dmitry Torokhov
Date: Wed May 21 2008 - 09:49:58 EST

On Tue, May 20, 2008 at 01:28:17PM +0200, Jean Delvare wrote:
> Hi Jonathan,
> On Tue, 20 May 2008 11:04:01 +0100, Jonathan Cameron wrote:
> > This email is basically a request for opinions on how and where such sensors
> > should be integrated into the kernel.
> >
> > To set the scene...
> >
> > Increasing numbers of embedded devices are being supplied attached MEMS
> > devices ( imote2 etc). Along with more traditional sensors such
> > as ADC's not being used for hardware monitoring, these do not really
> > seem to
> > fit with in an particular subsystem of the kernel. A previous
> > discussion on
> > lkml in 2006 considered the accelerometers to be found within some laptop
> > hard drives, but I haven't been able to track down any more general
> > discussions
> > of such non hardware monitoring sensors.
> >
> > The obvious possibilities are:
> >
> > * To place the various drivers within the spi / i2c etc subsystems as
> > relevant.
> Bad idea. Grouping drivers by connectivity is almost always the wrong
> thing to do, as it means that different persons will maintain them and
> they have all chances to diverge. You really want to group drivers by
> functionality. On top of that, I am busy enough maintaining the i2c
> core and bus drivers without having more i2c device drivers added to my
> plate. These days I am trying to _empty_ drivers/i2c/chips, if anything.
> > * To place within the hwmon subsystem as this is probably closest.
> > (there is already at least one straight ADC driver in hwmon)
> Probably not the wisest choice, if nothing else, because the hwmon
> maintainer is already overloaded. And I don't think that these devices
> have much in common with the traditional hardware monitoring components
> anyway.
> I'm not sure what "straight ADC driver" you are referring to, but
> anything which measures a voltage and exports the reading to user-space
> is, well, a voltage sensor, and thus fix within hwmon. If the same chip
> is used for a higher-level, dedicated function then we would probably
> have a separate driver for it, outside of hwmon.
> > * To create a new subsystem, or perhaps merely sysfs class to contain these
> > elements.
> Would be OK. Or:
> * Place these within the input subsystem. You might want to discuss
> this with the input subsystem maintainer Dmitry Torokhov (Cc'd). The
> Wii remote is essentially a joystick, and joysticks belong to the input
> subsystem.

I don't think that input subsystem woudl be the best choice. While we
do support the event-driven mechanism for delivering information to
userspace input is mostly oriented for human interface devices, not
general data acquisition. If anything input_dev is too fat. Another
thing is that input layer anonymizes input devices, makes them
capability-oriented. I.e. we dont really care what model of joystick
we have, we want something that reports ABS_X, ABS_Y, BTN_FIRE and
userpsace can use it whether it a simple analog joystick or something
fancy and USB connected. For your purposes you probably do want to know
what the device is and what exactly being sampled/measured.

I'd go with a lean and mean new subsytem.

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