linux-kernel - Re: [PATCH 1/3] dt-bindings: added new pwm-sifive driver documentation

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Message-ID: <20180430094205.GB2476@ulmo>
Date:   Mon, 30 Apr 2018 11:42:05 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     "Wesley W. Terpstra" <wesley@...ive.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Andreas Färber <afaerber@...e.de>,
        Noralf Trønnes <noralf@...nnes.org>,
        David Lechner <david@...hnology.com>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        SZ Lin <sz.lin@...a.com>, linux-pwm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] dt-bindings: added new pwm-sifive driver
 documentation

On Fri, Apr 27, 2018 at 03:59:56PM -0700, Wesley W. Terpstra wrote:
> Document new PWM device tree bindings for SiFive SoCs.
> 
> Signed-off-by: Wesley W. Terpstra <wesley@...ive.com>
> ---
>  .../devicetree/bindings/pwm/pwm-sifive.txt         | 28 ++++++++++++++++++++++
>  1 file changed, 28 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..7cea20d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt
> @@ -0,0 +1,28 @@
> +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 "sifive,pwm0"
> +- reg: physical base address and length of the controller's registers
> +- clocks: The frequency the controller runs at

That's not quite correct. According to the example below, this is a
phandle to the clock that drives the PWM at a given frequency.

> +- #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
> +- interrupts: one interrupt per PWM channel (currently unused in the driver)

Those parentheses provide information that doesn't belong in tha DT
bindings. What you this binding is used in a different operating system
that does use the interrupts?

Thierry

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