linux-kernel - Re: [PATCH 4/7] dt-bindings: Input: introduce new clock vibrator bindings

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Date:   Tue, 07 Jan 2020 09:52:21 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Brian Masney <masneyb@...tation.org>
Cc:     dmitry.torokhov@...il.com, robh+dt@...nel.org,
        mark.rutland@....com, agross@...nel.org,
        bjorn.andersson@...aro.org, mturquette@...libre.com,
        linux-input@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [PATCH 4/7] dt-bindings: Input: introduce new clock vibrator bindings

Quoting Brian Masney (2020-01-07 04:03:17)
> On Sun, Jan 05, 2020 at 12:35:33AM -0800, Stephen Boyd wrote:
> > Quoting Brian Masney (2019-12-04 16:25:00)
> > > +examples:
> > > +  - |
> > > +    #include <dt-bindings/clock/qcom,mmcc-msm8974.h>
> > > +    #include <dt-bindings/gpio/gpio.h>
> > > +
> > > +    vibrator {
> > > +        compatible = "clk-vibrator";
> > > +
> > > +        vcc-supply = <&pm8941_l19>;
> > > +
> > > +        clocks = <&mmcc CAMSS_GP1_CLK>;
> > > +        clock-names = "core";
> > > +        clock-frequency = <24000>;
> > > +
> > > +        enable-gpios = <&msmgpio 60 GPIO_ACTIVE_HIGH>;
> > > +
> > > +        pinctrl-names = "default";
> > > +        pinctrl-0 = <&vibrator_pin>;
> > 
> > I'm still trying to wrap my head around this. I think we can have a pwm
> > provider in a clk controller node (so imagine &mmcc has #pwm-cells) and
> > then this 'clk-vibrator' binding wouldn't exist? Instead we would have
> > some sort of binding for a device that expects a pwm and whatever else
> > is required, like the enable gpio and power supply. Is there an actual
> > hardware block that is this way? Does it have a real product id and is
> > made by some company? Right now this looks a little too generic to not
> > just be a catch-all for something that buzzes.
> 
> So have some of the Qualcomm clocks like this one register with both the
> clk and the pwm frameworks? I feel that approach would better represent
> the hardware in device tree.

That is one option. Or another option would be to have another node that
"adapts" a clk signal to a pwm provider. Similar to how we adapt a gpio
to make a clk gate or mux. Something like:

	gcc: clock-controller@...d {
		reg = <0xf00d 0xd00d>;
		#clock-cells = <1>;
	};


	pwm {
		compatible = "pwm-clk";
		#pwm-cells = <0>;
		clocks = <&gcc 45>;
		assigned-clocks = <&gcc 45>;
		assigned-clock-rates = <1400000>;
	};

And then the pwm-clk driver would adjust the duty cycle to generate a
pwm.

> 
> If we did that, then the pwm-vibra driver in the input subsystem could
> be used.