linux-kernel - Re: [PATCHv2 2/2] pwm: imx: support polarity inversion

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Message-ID: <20140123123341.GW15937@n2100.arm.linux.org.uk>
Date:	Thu, 23 Jan 2014 12:33:41 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Lothar Waßmann <LW@...O-electronics.de>
Cc:	Mark Rutland <mark.rutland@....com>, linux-pwm@...r.kernel.org,
	Sascha Hauer <kernel@...gutronix.de>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...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: [PATCHv2 2/2] pwm: imx: support polarity inversion

On Thu, Jan 23, 2014 at 11:52:03AM +0000, Russell King - ARM Linux wrote:
> On Thu, Jan 23, 2014 at 08:37:14AM +0100, Lothar Waßmann wrote:
> > This wouldn't buy much without a material change to of_pwm_get().
> > The function of_parse_phandle_with_args() called by of_pwm_get()
> > requires the number of args in the pwms property be greater or equal to
> > the #pwm-cells property in the pwm node. Thus, the interesting case of
> > having #pwm-cells = <3> without changing the existing users is
> > prohibited by of_parse_phandle_with_args().
> 
> I really don't think that's a problem we need to be concerned with at
> the moment.  What we need is for the kernel to be able to parse files
> with #pwm-cells = <2> with the pwms property containing two arguments,
> and when they're updated to #pwm-cells = <3> with the pwms property
> containing three arguments.
> 
> Yes, that means all the board dt files need to be updated at the same
> time to include the additional argument, but I don't see that as a big
> problem.
> 
> What we do need to do is to adjust the PWM parsing code such that it's
> possible to use either specification without causing any side effects.
> 
> I would test this, but as u-boot is rather fscked at the moment and the
> networking has broken on my cubox-i as a result... and it seems that the
> u-boot developers have pissed off cubox-i u-boot hackers soo much that
> they've dropped u-boot in favour of barebox...

Oh, and another reason... the u-boot video settings are totally and utterly
buggered to the point that it doesn't produce correct timings, and it seems
that u-boot people have zero interest in fixing that, so u-boot mainline is
basically refusing to fix this - another reason to stay away from it.

(1024x768 @ 60Hz produces 70Hz refresh on iMX6Q here - I've seen it produce
51Hz on iMX6S, both of which are far enough out that lots of display devices
will not accept it as a valid signal.)

-- 
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Estimate before purchase was "up to 13.2Mbit".
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