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

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Message-ID: <20190115201149.ghddnf27s5kqephc@pengutronix.de>
Date:   Tue, 15 Jan 2019 21:11:49 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
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,
        robh+dt@...nel.org, mark.rutland@....com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        sachin.ghadi@...ive.com, paul.walmsley@...ive.com
Subject: Re: [PATCH 1/2] pwm: sifive: Add DT documentation for SiFive PWM
 Controller

Hello,

this is v3, right? It is helpful to point this out to ease reviewing.

On Fri, Jan 11, 2019 at 01:52:43PM +0530, Yash Shah wrote:
> DT documentation for PWM controller added with updated compatible
> string.

Not sure what was updated here. But assuming this is compared to v2 this
is not a helpful info in the commit log.

> 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         | 37 ++++++++++++++++++++++
>  1 file changed, 37 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..e0fc22a
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt
> @@ -0,0 +1,37 @@
> +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: Please refer to sifive-blocks-ip-versioning.txt

While the description was too verbose in v2, this is too short. You
should at least mention something like "sifive,pwmX" and
"sifive,$cpuname-pwm" (or how ever that scheme works).

> +- reg: physical base address and length of the controller's registers
> +- clocks: Should contain a clock identifier for the PWM's parent clock.
> +- #pwm-cells: Should be 2.
> +  The first cell is the PWM channel number
> +  The second cell is the PWM polarity

I'd drop these two lines and refer to bindings/pwm/pwm.txt instead.

> +- sifive,approx-period-ns: the driver will get as close to this period as it can

As already said for v2: I'd drop "approx-". 

> +- 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-ns = <1000000>;
> +};
> -- 
> 1.9.1
> 
> 

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