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

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Message-ID: <20140113132625.4409abfc@ipc1.ka-ro>
Date:	Mon, 13 Jan 2014 13:26:25 +0100
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	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

Hi,

Arnd Bergmann wrote:
> 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.
> 
Good point. I'll try to change the driver to cope with either binding,
so the changes to the dts files of the current users will not be
necessary.


Lothar Waßmann
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