linux-kernel - Re: Sensors and the input layer (was Re: [RFC] [PATCH V2 1/2] input: CMA3000 Accelerometer driver)

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Message-ID: <20100924130241.GB1810@ucw.cz>
Date:	Fri, 24 Sep 2010 15:02:41 +0200
From:	Pavel Machek <pavel@....cz>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Felipe Balbi <me@...ipebalbi.com>, Hemanth V <hemanthv@...com>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"igor.stoppa@...ia.com" <igor.stoppa@...ia.com>,
	"kai.svahn@...ia.com" <kai.svahn@...ia.com>,
	"matthias.nyman@...ia.com" <matthias.nyman@...ia.com>
Subject: Re: Sensors and the input layer (was Re: [RFC] [PATCH V2 1/2]
 input: CMA3000 Accelerometer driver)

Hi!

> > So a voltmeter really makes no sense. It's not a set of keys and it
> > doesn't give X/Y/Z style readings. Nor does a camera. But a lot of things
> > do fit this to varying degrees.
> > 
> > I'm actually more dubious than Linus about ALS - because ALS tends not
> > produce 'events' but to be sampled, and there are significant power
> > implications to unnecessary polling.

That's very similar to analog joysticks, no?

> > And the more it's used the less special
> > code is needed in user or kernel space for PDAs and phones - instead they
> > just work.
> 
> OK, so let's say we start moving some of the devices into input. Which
> ones we consider suitable for input? I guess some 3-digit
> accelerometers, what else? Also, what new event types would we need?
> Let's take GPS - I do not think that ABS_X and ABS_Y are the best events
> to be used for such devices: I am trying to allow applications being

I'd not put GPS into input; yes, they do present 'x,y,z' in meters,
but that's not what users want. 'lat,lon,alt' is better, but it is
actually 'lat,lon,herror,alt,verror,time' and a lot of other
metadata...

Also, we already have driver for GPSes, its called gpsd. I'd leave
GPSes out of input.

> Also, GPS, liek ALS, would probably be polling, no?

Normally, GPS just sends you position info once a second.

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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