Re: [PATCH v3 3/6] dt-bindings: add binding for Sitronix ST7586 display panels

[David Lechner]

On 08/04/2017 09:54 AM, Laurent Pinchart wrote:
> Hi David,
>
> Thank you for the patch.
>
> On Thursday 03 Aug 2017 17:33:47 David Lechner wrote:
> > This adds a new binding for Sitronix ST7586 display panels.
> >
> > Using lego as the vendor prefix in the compatible string because the display
> > panel I am working with is an integral part of the LEGO MINDSTORMS EV3.
> >
> > Signed-off-by: David Lechner <david@xxxxxxxxxxxxxx>
> > ---
> >   .../bindings/display/sitronix,st7586.txt           | 26 +++++++++++++++++++
> >   1 file changed, 26 insertions(+)
> >   create mode 100644
> > Documentation/devicetree/bindings/display/sitronix,st7586.txt
> >
> > diff --git a/Documentation/devicetree/bindings/display/sitronix,st7586.txt
> > b/Documentation/devicetree/bindings/display/sitronix,st7586.txt new file
> > mode 100644
> > index 0000000..dfb0b7b
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/display/sitronix,st7586.txt
> > @@ -0,0 +1,26 @@
> > +Sitronix ST7586 display panel
> > +
> > +Required properties:
> > +- compatible:	"lego,ev3-lcd".
> > +
> > +The node for this driver must be a child node of a SPI controller, hence
> > +all mandatory properties described in ../spi/spi-bus.txt must be specified.
> > +
> > +Optional properties:
> > +- dc-gpios:	D/C pin. The presence/absence of this GPIO determines
> > +		the panel interface operation mode (IF[3:1] pins):
> > +		- present: IF=011 4-wire 8-bit data serial interface
> > +		- absent:  IF=010 3-wire 9-bit data serial interface
>
> How does this work ? Do you have a single GPIO on your system connected to
> IF[1], with IF[3:2] hardwired to 01 ?

LEGO has not made the internals of the display publicly available, so I 
cannot say for sure. But I assume that IF[3:1] is hardwired to 011. This 
causes pin D1 to assigned to the signal A0, which is what we are calling 
the dc gpio here.

If IF[3:1] were hardwired to 010, then pin D1 would be not not used and 
there would be no A0 signal.

So, basically, we can infer the state of IF[3:1] by the fact that we 
have a dc pin or not.

> > +- reset-gpios:	Reset pin
> > +- power-supply:	A regulator node for the supply voltage.
> > +- backlight:	phandle of the backlight device attached to the panel
> > +- rotation:	panel rotation in degrees counter clockwise (0,90,180,270)
>
> Please use the OF graph DT bindings (a.k.a. ports) to describe the connection
> between the panel and its source.

I am afraid that I do not understand this request. What would the source 
of the panel be? There is nothing like a SoC LCD controller that is 
driving this panel.

> > +Example:
> > +	display@0{
> > +		compatible = "lego,ev3-lcd";
> > +		reg = <0>;
> > +		spi-max-frequency = <10000000>;
> > +		dc-gpios = <&gpio 43 GPIO_ACTIVE_HIGH>;
> > +		reset-gpios = <&gpio 80 GPIO_ACTIVE_HIGH>;
> > +	};