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

From: David Lechner
Date: Fri Aug 04 2017 - 11:51:45 EST

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

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.

+ 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>;
+ };