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

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Date:   Tue, 18 Dec 2018 11:20:31 -0600
From:   Rob Herring <robh@...nel.org>
To:     Yash Shah <yash.shah@...ive.com>
Cc:     palmer@...ive.com, linux-pwm@...r.kernel.org,
        linux-riscv@...ts.infradead.org, thierry.reding@...il.com,
        mark.rutland@....com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, sachin.ghadi@...ive.com,
        paul.walmsley@...ive.com
Subject: Re: [RFC v2 1/2] pwm: sifive: Add DT documentation for SiFive PWM
 Controller

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.

This should reference the common doc Paul has written and not re-explain 
the versioning scheme again.

> +- reg: physical base address and length of the controller's registers
> +- clocks: The frequency the controller runs at
> +- #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

Needs a unit suffix as defined in property-units.txt

> +- 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>;
> +};
> -- 
> 1.9.1
>