linux-kernel - Re: [PATCH 2/3] dt-bindings: gpio: Add binding document for xylon logicvc-gpio

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Date:   Mon, 23 Sep 2019 16:13:04 +0200
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Rob Herring <robh@...nel.org>
Cc:     linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 2/3] dt-bindings: gpio: Add binding document for xylon
 logicvc-gpio

Hi,

On Fri 13 Sep 19, 15:36, Rob Herring wrote:
> On Tue, Sep 10, 2019 at 05:28:54PM +0200, Paul Kocialkowski wrote:
> > The Xylon LogiCVC display controller exports some GPIOs, which are
> > exposed as a dedicated driver.
> > 
> > This introduces the associated device-tree bindings documentation.
> > 
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > ---
> >  .../bindings/gpio/xylon,logicvc-gpio.txt      | 48 +++++++++++++++++++
> >  1 file changed, 48 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/gpio/xylon,logicvc-gpio.txt
> 
> Please consider using the new DT schema format.

Sure, I will give it a try.

> > diff --git a/Documentation/devicetree/bindings/gpio/xylon,logicvc-gpio.txt b/Documentation/devicetree/bindings/gpio/xylon,logicvc-gpio.txt
> > new file mode 100644
> > index 000000000000..4835659cb90b
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/gpio/xylon,logicvc-gpio.txt
> > @@ -0,0 +1,48 @@
> > +Xylon LogiCVC GPIO controller
> > +
> > +The Xylon LogiCVC is a display controller that contains a number of GPIO pins,
> > +meant to be used for controlling display-related signals.
> > +
> > +In practice, the GPIOs can be used for any purpose they might be needed for.
> > +
> > +The controller exposes GPIOs from the display and power control registers,
> > +which are mapped by the driver as follows:
> > +- GPIO[4:0] (display control) mapped to index 0-4
> > +- EN_BLIGHT (power control) mapped to index 5
> > +- EN_VDD (power control) mapped to index 6
> > +- EN_VEE (power control) mapped to index 7
> > +- V_EN (power control) mapped to index 8
> > +
> > +The driver was implemented and tested for version 3.02.a of the controller,
> > +but should be compatible with version 4 as well.
> > +
> > +Required properties:
> > +- compatible: Should contain "xylon,logicvc-3.02.a-gpio".
> > +- gpio-controller: Marks the device node as a gpio controller.
> > +- #gpio-cells: Should be 2. The first cell is the pin number and
> > +  the second cell is used to specify the gpio polarity:
> > +    0 = Active high,
> > +    1 = Active low.
> 
> No need to define these standard flags again here.
> 
> > +- gpio,syscon-dev: Syscon phandle representing the logicvc instance.
> 
> Don't need this. It's the parent.

Note that this is de-facto already supported by the gpio-syscon driver: the
driver supports either an explicit syscon dev with this property or having the
parent as syscon.

I assumed that mentioning both was good for the sake of diversity, but let's
stick to parent node then.

> > +
> > +Example:
> > +
> > +	logicvc: logicvc@...00000 {
> > +		compatible = "syscon", "simple-mfd";
> 
> This device needs a device specific compatible. These 2 alone are not 
> desired.

Thanks for the heads-up. I'll introduce a new compatible, describing a mfd
device then.

> Please define everything that's in the chip as much as you can. 
> 
> > +		reg = <0x43c00000 0x6000>;
> > +
> > +		#address-cells = <1>;
> > +		#size-cells = <1>;
> > +
> > +		logicvc_gpio: display-gpio@40 {
> 
> Use standard node names: gpio@40
> 
> You may not even need a child node here. It depends on what other child 
> nodes you have and whether they have their own DT resources.
> 
> > +			compatible = "xylon,logicvc-3.02.a-gpio";
> > +			reg = <0x40 0x40>;
> > +			gpio-controller;
> > +			#gpio-cells = <2>;
> > +			gpio,syscon-dev = <&logicvc>;
> > +		};
> > +	};
> > +
> > +Note: the device-tree node should either be declared as a child of the logicvc
> > +syscon node or the syscon node should be precised with the gpio,syscon-dev
> > +property. Both are shown in the example above.
> 
> Why? Just pick one and a child node is the preference.

That was for the sake of diversity, but having both at once could probably be
misleading too.

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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