On 08/04/2017 02:39 PM, Laurent Pinchart wrote:

Hi David,

On Friday 04 Aug 2017 10:51:37 David Lechner wrote:

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On 08/04/2017 09:54 AM, Laurent Pinchart wrote:

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On Thursday 03 Aug 2017 17:33:47 David Lechner wrote:

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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@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.

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+- 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)

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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.

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+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>;
+	};