linux-kernel - Re: [PATCH 1/2] PWM: let of_xlate handlers check args count

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Message-ID: <20140123165349.GY15937@n2100.arm.linux.org.uk>
Date:	Thu, 23 Jan 2014 16:53:50 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	Lothar Waßmann <LW@...O-electronics.de>,
	Mark Rutland <mark.rutland@....com>, linux-pwm@...r.kernel.org,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Rob Landley <rob@...dley.net>,
	Kumar Gala <galak@...eaurora.org>,
	Shawn Guo <shawn.guo@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] PWM: let of_xlate handlers check args count

On Thu, Jan 23, 2014 at 12:04:44PM +0100, Sascha Hauer wrote:
> On Thu, Jan 23, 2014 at 11:56:32AM +0100, Lothar Waßmann wrote:
> > Hi,
> > 
> > Sascha Hauer wrote:
> > > of_pwm_n_cells for the of_xlate handler is stored in struct pwm_chip,
> > > but it is only ever used by the of_xlate handler itsel. Remove
> > > of_pwm_n_cells from struct pwm_chip and let the handler do the argument
> > > count checking to simplify the code.
> > > 
> > This still does not make the PWM_POLARITY flag in the pwms node
> > optional as was the goal because of_parse_phandle_with_args() requires
> > at least #pwm-cells arguments in the node.
> > 
> > So, with a DT configuration like:
> > pwm0: pwm@0 {
> > 	#pwm-cells = <3>;
> > };
> > backlight {
> > 	pwms = <&pwm0 0 100000>;
> > };
> 
> We misunderstood each other. My goal was to allow the driver to also
> work with old devicetrees which specify #pwm-cells = <2>, not to allow
> inconsistent devicetrees like the snippet above.

In which case, the patch I've posted seems to do that job too... I'm
just about to test out the three-cell version.

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