linux-kernel - Re: [RFC v2 1/2] pwm: sifive: Add DT documentation for SiFive PWM Controller

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Message-ID: <CAJ2_jOGBK6OtXe0UO6nYc1KPDVi39NtD8f+hUkpxROhzukPw7w@mail.gmail.com>
Date:   Fri, 4 Jan 2019 10:39:20 +0530
From:   Yash Shah <yash.shah@...ive.com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Palmer Dabbelt <palmer@...ive.com>, linux-pwm@...r.kernel.org,
        linux-riscv@...ts.infradead.org,
        Thierry Reding <thierry.reding@...il.com>, robh+dt@...nel.org,
        mark.rutland@....com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sachin Ghadi <sachin.ghadi@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: Re: [RFC v2 1/2] pwm: sifive: Add DT documentation for SiFive PWM Controller

On Tue, Dec 18, 2018 at 2:46 AM Uwe Kleine-König
<u.kleine-koenig@...gutronix.de> wrote:
>
> On Fri, Dec 14, 2018 at 11:50:41AM +0530, Yash Shah wrote:
> > DT documentation for PWM controller added with updated compatible
> > string.
> >
> > Signed-off-by: Wesley W. Terpstra <wesley@...ive.com>
> > [Atish: Compatible string update]
> > Signed-off-by: Atish Patra <atish.patra@....com>
> > Signed-off-by: Yash Shah <yash.shah@...ive.com>
> > ---
> >  .../devicetree/bindings/pwm/pwm-sifive.txt         | 44 ++++++++++++++++++++++
> >  1 file changed, 44 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/pwm/pwm-sifive.txt
> >
> > diff --git a/Documentation/devicetree/bindings/pwm/pwm-sifive.txt b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt
> > new file mode 100644
> > index 0000000..250d8ee
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt
> > @@ -0,0 +1,44 @@
> > +SiFive PWM controller
> > +
> > +Unlike most other PWM controllers, the SiFive PWM controller currently only
> > +supports one period for all channels in the PWM. This is set globally in DTS.
> > +The period also has significant restrictions on the values it can achieve,
> > +which the driver rounds to the nearest achievable frequency.
> > +
> > +Required properties:
> > +- compatible: should be something similar to "sifive,<chip>-pwm" for
> > +           the PWM as integrated on a particular chip, and
> > +           "sifive,pwm<version>" for the general PWM IP block
> > +           programming model. Supported compatible strings are:
> > +           "sifive,fu540-c000-pwm" for the SiFive PWM v0 as
> > +           integrated onto the SiFive FU540 chip, and "sifive,pwm0"
> > +           for the SiFive PWM v0 IP block with no chip integration
> > +           tweaks.
> > +- reg: physical base address and length of the controller's registers
> > +- clocks: The frequency the controller runs at
>
> This is unusual and the example below lists a clock phandle (which is
> the common thing), so I guess the description is just wrong.

You are right, I will correct the description.

>
> > +- #pwm-cells: Should be 2.
> > +  The first cell is the PWM channel number
> > +  The second cell is the PWM polarity
> > +- sifive,approx-period: the driver will get as close to this period as it can
>
> What is the unit? I'd drop "approx", that the driver might not be able
> to exactly hit the specified period is (IMHO) obvious and doesn't need
> to be mentioned in the property name.

The unit is nanoseconds. Will add the unit suffix to the property name.

>
> > +- interrupts: one interrupt per PWM channel
> > +
> > +PWM RTL that corresponds to the IP block version numbers can be found
> > +here:
> > +
> > +https://github.com/sifive/sifive-blocks/tree/master/src/main/scala/devices/pwm
> > +
> > +Further information on the format of the IP
> > +block-specific version numbers can be found in
> > +Documentation/devicetree/bindings/sifive/sifive-blocks-ip-versioning.txt
> > +
> > +Examples:
> > +
> > +pwm:  pwm@...20000 {
> > +     compatible = "sifive,fu540-c000-pwm","sifive,pwm0";
> > +     reg = <0x0 0x10020000 0x0 0x1000>;
> > +     clocks = <&tlclk>;
> > +     interrupt-parent = <&plic>;
> > +     interrupts = <42 43 44 45>;
> > +     #pwm-cells = <2>;
> > +     sifive,approx-period = <1000000>;
> > +};
>
> Best regards
> Uwe

Thanks for the comments!

>
> --
> Pengutronix e.K.                           | Uwe Kleine-König            |
> Industrial Linux Solutions                 | http://www.pengutronix.de/  |