Re: [PATCH 3/7] gpio: mvebu: Add limited PWM support

[Thierry Reding <thierry.reding@gmail.com>]

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On Thu, Jan 15, 2015 at 10:52:51AM +0100, Linus Walleij wrote:
> On Tue, Jan 13, 2015 at 3:42 AM, Andrew Lunn <andrew@lunn.ch> wrote:
> 
> > So i thought about this some more. What would an MFD based solution
> > look like?
> >
> > First issue is backwards compatibility. There are currently around 90
> > .dts files using this gpio driver. I could imagine a few of these
> > being changed to make use of an MFD based driver to make us of the new
> > features, but the rest expect backwards compatibility.
> 
> Good point.
> 
> > I think the only sensible way to achieve this is that the gpio driver
> > keeps its existing binding.
> 
> Yup.
> 
> > This does not really describe the hardware. The hardware is more like:
> >
> >         gpio: gpio {
> >                 compatible = "marvell,orion-gpio";
> >                 reg = <0xd0018100 0x40>;
> >                 ngpios = <32>;
> >                 gio-controller;
> >                 #gpio-cells = <2>;
> >                 interrupt-controller;
> >                 #interrupt-cells = <2>;
> >                 interrupts = <16>, <17>, <18>, <19>;
> >                 clocks = <&coreclk 0>;
> >
> >                 pwm: pwm {
> >                         compatible = "marvell,armada-pwm";
> >                         reg = <0xd00181c0 0x08>;
> >                         #pwm-cells = <2>;
> >                         clocks = <&coreclk 0>;
> >                 };
> >         };
> >
> > but i don't think MFD supports that sort of structure?
> 
> No it would have to be some custom DT code in the GPIO driver
> spawning the PWM platform device.
> 
> I think it's better if we either go with the first solution of a combined
> GPIO+PWM node (it's also elegant in a way, and perfectly
> OK with device tree I think) but I want the PWM maintainer to
> say if it's OK to have a PWM driver inside a GPIO driver.

I'm fine with that, too. I'd request an update to MAINTAINERS so that at
least linux-pwm@vger.kernel.org gets included on patches against the
driver.

That said, the above DT description would lend itself nicely to MFD in
my opinion.

Thierry

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