linux-kernel - Re: [PATCH 2/2] pwm: imx: support polarity inversion

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Date:	Mon, 13 Jan 2014 12:13:58 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Lothar Waßmann <LW@...o-electronics.de>,
	Shawn Guo <shawn.guo@...aro.org>,
	Sascha Hauer <kernel@...gutronix.de>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Thierry Reding <thierry.reding@...il.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pwm@...r.kernel.org
Subject: Re: [PATCH 2/2] pwm: imx: support polarity inversion

On Monday 13 January 2014 11:29:48 Lothar Waßmann wrote:

> diff --git a/arch/arm/boot/dts/imx50.dtsi b/arch/arm/boot/dts/imx50.dtsi
> index 01c0499..e3647a8 100644
> --- a/arch/arm/boot/dts/imx50.dtsi
> +++ b/arch/arm/boot/dts/imx50.dtsi
> @@ -273,7 +273,7 @@
>  			};
>  
>  			pwm1: pwm@...b4000 {
> -				#pwm-cells = <2>;
> +				#pwm-cells = <3>;
>  				compatible = "fsl,imx50-pwm", "fsl,imx27-pwm";
>  				reg = <0x53fb4000 0x4000>;
>  				clocks = <&clks IMX5_CLK_PWM1_IPG_GATE>,
...
> @@ -271,6 +293,13 @@ static int imx_pwm_probe(struct platform_device *pdev)
>  		return PTR_ERR(imx->mmio_base);
>  
>  	data = of_id->data;
> +	if (data->output_polarity) {
> +		dev_info(&pdev->dev, "PWM supports inversion\n");
> +		imx_pwm_ops.set_polarity = imx_pwm_set_polarity;
> +		imx->chip.of_xlate = of_pwm_xlate_with_flags;
> +		imx->chip.of_pwm_n_cells = 3;
> +	}
> +
>  	imx->config = data->config;
>  	imx->set_enable = data->set_enable;

This looks like you are breaking compatibility with the binding,
which requires #pwm-cells to be <2>. You can extend the binding
to allow both <2> and <3>, but then you have to not only document
that change in the binding, but also ensure that the pwm driver
is able to use either variant.

	Arnd
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