linux-kernel - Re: [PATCH RESEND] LEDS-One-Shot-Timer-Trigger-implementation

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Date:	Tue, 10 Apr 2012 08:25:06 +1000
From:	NeilBrown <neilb@...e.de>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Shuah Khan <shuahkhan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	rpurdie@...ux.intel.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] LEDS-One-Shot-Timer-Trigger-implementation

On Sun, 8 Apr 2012 17:06:46 -0700 Dmitry Torokhov <dmitry.torokhov@...il.com>
wrote:

> On Mon, Apr 09, 2012 at 09:42:19AM +1000, NeilBrown wrote:

> > Also, I don't think 'ff' allows for "vibrate for N milliseconds".
> > It appears that one uses the "rumble" effect and have to say "turn it on",
> > then "turn it off".  Is that correct?
> 
> No, it is not.
> 
> > I found 'struct ff_replay' which has a 'length' which is a duration, but it
> > doesn't seem to be used.
> 
> It does, see drivers/input/ff-memless.c where it us used to schedule
> when effect starts and how long it should play. Non memoryless devices
> (such as iforce) are supposed to schedule effects themselves.
> 
> > 
> > How would you tell the force feedback framework to play the vibrator for
> > 120ms, then stop?
> 
> By specifying replay->length = 120

You seem to make a convincing case.  I'll explore this some more and see what
it is like in practice.

Clipping from above:

> 
> Well, if you consider "input" is really "hid" then FF is really
> appropriate for iterfacing with a human.
> 

A slightly related question.  My phone has accelerometers in it.  I want to
use them entirely a human-interface-devices.  The device itself can detect
inversions and taps and jerks and I want to report just those to user-space,
preferably via the input (aka hid :-) subsystem.  However my understanding is
that accelerometer drivers aren't welcome as input drivers.  Is that still
true?
There is nothing 'industrial' about these accelerometers so I would like to
avoid 'iio'.  What are your thoughts about this?

Thanks,
NeilBrown

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