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

[David Lechner]

On 08/04/2017 02:39 PM, Laurent Pinchart wrote:
> Hi David,
> 
> On Friday 04 Aug 2017 10:51:37 David Lechner wrote:
>> On 08/04/2017 09:54 AM, Laurent Pinchart wrote:
>>> 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 at lechnology.com>
>>>> ---
>>>>
>>>>    .../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.
> 
> OK, now I understand what you mean. Maybe you should phrase it a bit
> differently to make it clearer ? How about
> 
> dc-gpios: Specified or the GPIO connected to the panel's D/C pin (also called
> A0). The property is required when the panel operates in 4-wire mode (IF[3:1]
> = 011) and prohibited when the panel operates in 3-wire mode (IF[3:1] = 010).

Yes, this is more clear. Thank you for the suggestion.

> 
> By the way, if the signal is named A0, why don't you call the property a0-
> gpios ?

I consider "dc-gpios" to be a generic name since it is used by many 
different panels. But I would be OK with calling it "a0-gpios" as well. 
It will just require more explanation that this is the A0 *signal* and 
not the A0 *pin*. The actual pin used is labeled *D1* on the controller.

On the other hand, it is labeled as A0 on LEGO's schematic, so perhaps 
a0 is better.

> 
>>>> +- 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.
> 
> My bad, I should have read the panel datasheet before replying :-S Please
> ignore this comment.
> 
>>>> +Example:
>>>> +	display at 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>;
>>>> +	};
>