linux-kernel - Re: [PATCH v7 04/11] pwm: add DT bindings documentation for atmel-hlcdc-pwm driver

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Date:	Mon, 6 Oct 2014 12:33:26 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	David Airlie <airlied@...ux.ie>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Andrew Victor <linux@...im.org.za>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
	Rob Clark <robdclark@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mark Yao <mark.yao@...k-chips.com>
Subject: Re: [PATCH v7 04/11] pwm: add DT bindings documentation for
 atmel-hlcdc-pwm driver

On Mon, Oct 06, 2014 at 11:13:51AM +0100, Thierry Reding wrote:
> On Wed, Oct 01, 2014 at 04:53:01PM +0200, Boris Brezillon wrote:
> > From: Boris BREZILLON <boris.brezillon@...e-electrons.com>
> > 
> > The HLCDC IP available in some Atmel SoCs (i.e. sam9x5i.e. at91sam9n12,
> > at91sam9x5 family or sama5d3 family) provide a PWM device.
> > 
> > The DT bindings used for this PWM device is following the default 3 cells
> > bindings described in Documentation/devicetree/bindings/pwm/pwm.txt.
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> > ---
> >  .../devicetree/bindings/pwm/atmel-hlcdc-pwm.txt    | 55 ++++++++++++++++++++++
> >  1 file changed, 55 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/pwm/atmel-hlcdc-pwm.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/pwm/atmel-hlcdc-pwm.txt b/Documentation/devicetree/bindings/pwm/atmel-hlcdc-pwm.txt
> > new file mode 100644
> > index 0000000..86ad3e2
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/pwm/atmel-hlcdc-pwm.txt
> > @@ -0,0 +1,55 @@
> > +Device-Tree bindings for Atmel's HLCDC (High LCD Controller) PWM driver
> > +
> > +The Atmel HLCDC PWM is subdevice of the HLCDC MFD device.
> > +See ../mfd/atmel-hlcdc.txt for more details.
> > +
> > +Required properties:
> > + - compatible: value should be one of the following:
> > +   "atmel,hlcdc-pwm"
> > + - pinctr-names: the pin control state names. Should contain "default".
> > + - pinctrl-0: should contain the pinctrl states described by pinctrl
> > +   default.
> > + - #pwm-cells: should be set to 3. This PWM chip use the default 3 cells
> > +   bindings defined in Documentation/devicetree/bindings/pwm/pwm.txt.
> > +   The first cell encodes the PWM id (0 is the only acceptable value here,
> > +   because the chip only provide one PWM).
> > +   The second cell encodes the PWM period in nanoseconds.
> > +   The third cell encodes the PWM flags (the only supported flag is
> > +   PWM_POLARITY_INVERTED)
> 
> Given that this already refers to the default 3 cells binding it doesn't
> need to repeat part of the contents of pwm.txt.

Given that pwm.txt states:

pwm-specifier : array of #pwm-cells specifying the given PWM 
                (controller specific)

I'd leave it here. Just because pwm.txt gives an example of a controller
specific meaning for the pwm cells, I don't think we should rely on it
everywhere.

Mark.
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