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: <AANLkTims1CagvPZQjTmYrOVi8REeLVbyyt3kEY_tsCtx@mail.gmail.com>
Date:	Mon, 30 Aug 2010 14:28:37 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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)

On Monday, August 30, 2010, Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
>
> But do you believe that input should be the "primary residence" for the
> devices when they are only _sometimes_ used as input devices? Or it
> would make sense to employ a converter from XXX to input (either purely
> in-kernel or userspace over uinput)?

Umm... You've brought that up before as an objection, but what _is_
that other model that you would convert from? IOW what *is* that XXX
that you talk about?

So I think accelerometers etc should be seen as input devices for the
simple reason that

 (a) They really *are* input devices in all the most common cases. If
you have a phone with an accelerometer, it really is used as an input
device quite like a joystick.

The fact that there are specialized and rare cases where people may
have some fancier accelerometer that isn't necessarily seen that way,
and where it is used for some fancy scientific experiment or whatever
doesn't change this in *any* way. The common case that almost
everybody cares about - and that is getting more common - is the
simple and obvious input case.

How is a Wii accelerometer in any way different from a joystick? How
is a phone accelerometer any different from one? The answer is clear:
they aren't different! So it makes 100% sense to expose them under the
same subsystem.

(b) You cannot even name your XXX thing. It clearly makes sense (at
least within Tue context of a driver for some embedded phone chip) to
see it as an input device. And nothing else comes to mind. You'd have
to expose it as some random character device and then everybody would
just have to make it emulate an input device in user space anyway.
What's the point of that?

None. That's what the point is.

So I really don't understand why you're fighting the input device
angle. It makes sense as an input device. It does NOT make sense as
anything else.

Really - what else could a phone accelerometer (or GPS device, for
that matter) really be? It very much is about user input - even if it
isn't a keyboard.

            Linus
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