linux-kernel - Re: [PATCHv4 4/4] Documentation: Add device tree bindings for Freescale FTM PWM.

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Date:	Fri, 13 Sep 2013 16:34:18 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Xiubo Li <Li.Xiubo@...escale.com>,
	Linus Walleij <linus.walleij@...aro.org>
CC:	r65073@...escale.com, thierry.reding@...il.com,
	s.hauer@...gutronix.de, t.figa@...sung.com,
	grant.likely@...aro.org, linux@....linux.org.uk, rob@...dley.net,
	ian.campbell@...rix.com, mark.rutland@....com, pawel.moll@....com,
	rob.herring@...xeda.com, linux-arm-kernel@...ts.infradead.org,
	linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCHv4 4/4] Documentation: Add device tree bindings for Freescale
 FTM PWM.

On 09/12/2013 11:58 PM, Xiubo Li wrote:
> This adds the Document for Freescale FTM PWM driver under
> Documentation/devicetree/bindings/pwm/.

> diff --git a/Documentation/devicetree/bindings/pwm/pwm-fsl-ftm.txt b/Documentation/devicetree/bindings/pwm/pwm-fsl-ftm.txt

> +Required properties:

> +- clock-names : Includes the following module clock source entries:
> +    "ftm0" (system clock),
> +    "ftm0_fix_sel" (fixed frequency clock),
> +    "ftm0_ext_sel" (external clock)
> +- clocks : Must contain an entry list for entries in clock-names.

s/an entry list/a clock specifier/
s/for entries/for each entry/

> +- fsl,pwm-counter-clk: The FTM PWM counter clock source, should be one of the
> +  entries in clock-names.

So the IP block has 3 input clocks, and also a mux to select which one
to use? That sounds slightly unusual, but possible.

If there is really only 1 clock input to the IP block, and the mux is
part of some other module, then this binding should have only 1 entry in
clocks.

> +- For each channel's pinctrl, the "chN-active" and "chN-idle" states should be
> +  implemented at the same time.

I still don't believe that multiple pinctrl states active at once is
something that the pinctrl bindings conceptually support. CC+=LinusW, do
we want to allow this?

Assuming this is allowed, you'd want to write something more like the
following:

pinctrl-names: Must include "chN-active" and "chN-idle" for each channel
ID N in range 0..7.
pinctrl-NNN: One property must exist for each entry in pinctrl-names.
See ../pinctrl/pinctrl-bindings.txt for details of the property values.
> +Example:
> +
> +pwm0: pwm@...38000 {
> +		compatible = "fsl,vf610-ftm-pwm";
> +		reg = <0x40038000 0x1000>;
> +		#pwm-cells = <3>;
> +		clock-names = "ftm0", "ftm0_fix_sel", "ftm0_ext_sel";
> +		clocks = <&clks VF610_CLK_FTM0>,
> +			<&clks VF610_CLK_FTM0_FIX_SEL>,
> +			<&clks VF610_CLK_FTM0_EXT_SEL>;
> +		pinctrl-names = "ch0-active", "ch0-idle", "ch1-active", "ch1-idle",
> +		....;
> +		pinctrl-0 = <&pinctrl_pwm0_ch0_active>;
> +		pinctrl-1 = <&pinctrl_pwm0_ch0_idle>;
> +		pinctrl-2 = <&pinctrl_pwm0_ch1_active>;
> +		pinctrl-3 = <&pinctrl_pwm0_ch1_idle>;
> +		...
> +		fsl,pwm-counter-clk = "ftm0_ext_sel";
> +};

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