linux-kernel - Re: [PATCH v3 4/4] mvebu: wrt1900ac: Use pwm-fan rather than gpio-fan

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Date:   Mon, 27 Mar 2017 15:17:25 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Ralph Sennhauser <ralph.sennhauser@...il.com>
Cc:     linux-gpio@...r.kernel.org, Imre Kaloz <kaloz@...nwrt.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Courbot <gnurou@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jason Cooper <jason@...edaemon.net>,
        Gregory Clement <gregory.clement@...e-electrons.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Russell King <linux@...linux.org.uk>,
        linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 4/4] mvebu: wrt1900ac: Use pwm-fan rather than gpio-fan

On Sun, Mar 26, 2017 at 11:05:58PM +0200, Ralph Sennhauser wrote:
> On Fri, 24 Mar 2017 15:35:05 +0100
> Andrew Lunn <andrew@...n.ch> wrote:
> 
> > > +	pwm_fan {
> > >  		/* SUNON HA4010V4-0000-C99 */
> > > -		compatible = "gpio-fan";
> > > -		gpios = <&gpio0 24 0>;
> > >  
> > > -		gpio-fan,speed-map = <0    0
> > > -				      4500 1>;
> > > +		compatible = "pwm-fan";
> > > +		pwms = <&gpio0 24 4000 0>;  
> > 
> > Hi Ralph
> > 
> > I believe this last 0 is the flags parameter. Now that we have
> > #pwm-cells = 1, i think this last 0 should be dropped.
> > 
> > 	  Andrew
> 
> Hi Andrew,
> 
> isn't the 4000 (period?) pwm-cell #2 and 0 (flags?) pwm-cell #3? I
> actually expect "pwms = <&gpio0 24>;" here or "#pwm-cells = <2>;"

Hi Ralph

>From Documentation/devicetree/bindings/pwm/pwm.txt:

        pwm-list ::= <single-pwm> [pwm-list]
        single-pwm ::= <pwm-phandle> <pwm-specifier>
        pwm-phandle : phandle to PWM controller node
        pwm-specifier : array of #pwm-cells specifying the given PWM
                        (controller specific)

Our pwm-list has a single single-pwm.
phandle is &gpio0.
The remaining parts are the specifier, or which there should be #pwm-calls.

>From Documentation/devicetree/bindings/pwm/pwm.txt again:

pwm-specifier typically encodes the chip-relative PWM number and the PWM
period in nanoseconds.

Optionally, the pwm-specifier can encode a number of flags (defined in
<dt-bindings/pwm/pwm.h>) in a third cell:
- PWM_POLARITY_INVERTED: invert the PWM signal polarity

So we are using the 24th PWM and 4000 nanosecod period. We don't want
any flags.

So

pwms = <&gpio0 24 4000>;  

has a phandle, and then 2 cells.

    Andrew