linux-kernel - Re: [PATCHv4 1/3] dt-bindings: input: add pwm-vibrator

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Message-ID: <20170725085949.2v3b373p5xkje47a@earth>
Date:   Tue, 25 Jul 2017 10:59:49 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.co.uk>
To:     Pavel Machek <pavel@....cz>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Rob Herring <robh+dt@...nel.org>, linux-input@...r.kernel.org,
        linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 1/3] dt-bindings: input: add pwm-vibrator

Hi,

On Mon, Jul 24, 2017 at 09:20:17PM +0200, Pavel Machek wrote:
> On Fri 2017-07-14 12:01:49, Sebastian Reichel wrote:
> > Add DT binding document for PWM controlled vibrator devices.
> > 
> > Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.co.uk>
> 
> Acked-by: Pavel Machek <pavel@....cz>
> 
> > index 000000000000..09145d18491d
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/input/pwm-vibrator.txt
> > @@ -0,0 +1,66 @@
> > +* PWM vibrator device tree bindings
> > +
> > +Registers a PWM device as vibrator. It is expected, that the vibrator's
> > +strength increases based on the duty cycle of the enable PWM channel
> > +(100% duty cycle meaning strongest vibration, 0% meaning no vibration).
> > +
> > +The binding supports an optional direction PWM channel, that can be
> > +driven at fixed duty cycle. If available this is can be used to increase
> > +the vibration effect of some devices.
> 
> Actually what "direction" does would be nice to explain, because I
> don't know. Does it make the motor turn the other way around?

Yes, at least that's how I understand it. IIUIC this will increase
the imbalance effect and thus the vibration.

> > +Required properties:
> > +- compatible: should contain "pwm-vibrator"
> 
> should->Should.
>
> > +- pwm-names: Should contain "enable" and optionally "direction"
> > +- pwms: Should contain a PWM handle for each entry in pwm-names
> > +
> > +Optional properties:
> > +- vcc-supply: Phandle for the regulator supplying power
> > +- direction-duty-cycle-ns: Duty cycle of the direction PWM channel in
> > +                           nanoseconds, defaults to 50% of the channel's
> > +			   period.
> 
> Is nanoseconds right unit here? It drives a motor...

Yes, for the driving the motor the values will be very big
and we could use milliseconds. But the PWM specifier [0] uses
nanoseconds for the period and I think period and duty cycle
should be described in the same scale.

[0] Documentation/devicetree/bindings/pwm/pwm.txt

-- Sebastian

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