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

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Message-ID: <1333995365.2871.17.camel@lorien2>
Date:	Mon, 09 Apr 2012 12:16:05 -0600
From:	Shuah Khan <shuahkhan@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	shuahkhan@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
	neilb@...e.de, rpurdie@...ux.intel.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] LEDS-One-Shot-Timer-Trigger-implementation

On Mon, 2012-04-09 at 10:37 -0700, Dmitry Torokhov wrote:
> On Mon, Apr 09, 2012 at 10:55:49AM -0600, Shuah Khan wrote:
> > On Sat, 2012-04-07 at 14:56 -0700, Dmitry Torokhov wrote:
> > > Hi Shuah,
> > > 
> > > On Sat, Apr 07, 2012 at 08:13:44AM -0600, Shuah Khan wrote:
> > > > 
> > > > > > +This feature will help implement vibrate functionality which requires one
> > > > > > +time activation of vibrate mode without a continuous vibrate on/off cycles.
> > > > > 
> > > > > They make vibrating LED? ;)
> > > > > 
> > > > > What's going on here?  You're proposing to repurpose the LEDs code to
> > > > > drive vibration devices?  Or some devices couple a LED with a vibration
> > > > > device?
> > > > 
> > > > I owe you filling in the blanks type explanation. Let me describe the
> > > > use-case I am trying to address first. Vibrater function on phones is
> > > > implemented using PWM pins on SoC or PMIC. When there is no such
> > > > hardware present, a software solution is needed. Currently two drivers
> > > > timed-gpio and timed-output (under staging/android in Linux 3.3)
> > > > together implement the software vibrate feature. The main functionality
> > > > it implements is the one time enables of timer to prevent user space
> > > > crashes leaving the phone in vibrate mode causing the battery to drain.
> > > > leds as it is implemented currently, is not suitable to address this
> > > > use-case as it doesn't support one time enables.
> > > 
> > > So why do not you use memoryless force feedback framework that other
> > > devices use (see drivers/input/misc/*vibra.c drivers).
> > > 
> > 
> > Dimitry,
> > 
> > I took a look at these vibra* drivers. The three vibrate drivers are
> > chip-set specific. The use-case I have is a non-chip set approach to
> > address the use-case when vibrate hardware is not present. Are you
> > envisioning a generic approach using ff-memoryless infrastructure?
> 
> Shuah,
> 
> I guess I am confused now. You need some form of hardware to make your
> device to vibrate.
> 
> What exactly are you trying to do? Are you trying to:
> 
> 1. activate vibration on devices that can actually do it using LED
>    interface, or
> 
> 2. use LEDs as an alternative to vibrate on devices that can't
>    physically vibrate?
> 
> Thanks.

What I meant by generic approach is a higher level interface that is not
tied too closely to the underlying hardware. Similar to the leds-pwm.c
and leds-gpio.c handle gpio and pwm based leds. The vibrate hardware in
my sue-case is a gpio based and could pwm based on some phones.

-- Shuah


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