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Date:   Tue, 29 Aug 2017 22:38:46 +0200
From:   Pavel Machek <>
To:     Jacek Anaszewski <>
Cc:,,, Andrew Morton <>,
Subject: Re: [PATCH] Documentation: small fixes for LEDs, hide notes about


> > -As a specific example of this use-case, let's look at vibrate feature on
> > -phones. Vibrate function on phones is implemented using PWM pins on SoC or
> > -PMIC. There is a need to activate one shot timer to control the vibrate
> > -feature, to prevent user space crashes leaving the phone in vibrate mode
> > -permanently causing the battery to drain.
> I'm not sure if it is a good idea to remove this description. Users will
> still be able to use transient trigger this way. It has been around for
> five years already and there are users which employ it in this
> particular way [0].

I am. Yes, people were doing that, but no, vibration motor is not a
LED. PWM behaviour is different, for example, motor is likely to stop
at low PWM values. We do not want people to do that.

> Apart from that it's the only documented kernel API for vibrate devices

Input subsystem has force-feedback protocol, which is very often just
vibrations. Documentation/input/ff.rst . Nokia N900 phone actually
uses that API.
(cesky, pictures)

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