[PATCH 2/6] dt-bindings/display: Add Solomon SSD16xx e-paper controller binding

[Devarsh Thakkar <devarsht@ti.com>]

Add device tree binding for the Solomon Systech SSD16xx family of e-Paper
display controllers (SSD1683 [1], SSD1673 [3], SSD1680 [4], SSD1681 [5]).

The binding covers the 4-wire SPI interface with required GPIO pins for
reset (active-low), busy status (active-high), and data/command selection.
The spi-max-frequency is capped at 20 MHz per the SSD1683 datasheet [1]
which is also the maximum supported frequency amongst the family.

An optional rotation property allows static display orientation to be
configured from device tree.

The data/command selection GPIO pin is also kept as optional since various
SSD16XX controllers such as SSD1683 [1] support 3-wire mode too with
data/command selection bit transmitted as first bit before sending the data
sequence.

The first supported compatible is for Gooddisplay GDEY042T81 which is 4.2",
400x300 resolution black/white e-paper display using SSD1683 controller.

Links:
[1] : https://www.crystalfontz.com/controllers/SolomonSystech/SSD1683
[2] : https://files.seeedstudio.com/wiki/Other_Display/42-epaper/GDEY042T81.pdf
[3] : https://www.crystalfontz.com/controllers/SolomonSystech/SSD1673
[4] : https://www.crystalfontz.com/controllers/SolomonSystech/SSD1680
[5] : https://www.crystalfontz.com/controllers/SolomonSystech/SSD1681

Signed-off-by: Devarsh Thakkar <devarsht@ti.com>
---
 .../bindings/display/solomon,ssd16xx.yaml     | 81 +++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/solomon,ssd16xx.yaml

diff --git a/Documentation/devicetree/bindings/display/solomon,ssd16xx.yaml b/Documentation/devicetree/bindings/display/solomon,ssd16xx.yaml
new file mode 100644
index 000000000000..2433ddb859d6
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/solomon,ssd16xx.yaml
@@ -0,0 +1,81 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/solomon,ssd16xx.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Solomon Systech SSD16xx controller based e-paper display panels
+
+maintainers:
+  - Devarsh Thakkar <devarsht@ti.com>
+
+description:
+  The SSD16xx family includes e-paper display controllers (SSD1680, SSD1681,
+  SSD1673, SSD1683) with integrated gate driver, source driver and timing controller.
+  Different panels use these controllers in monochrome or 3-color configurations.
+  The controller uses a 4-wire SPI interface and requires GPIO pins for reset,
+  busy status, and data/command control with a 3-wire mode also available
+  where D/C bit is transmitted along the SPI data line before sending actual data.
+
+allOf:
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
+
+properties:
+  compatible:
+    enum:
+      - gooddisplay,gdey042t81  # 4.2" 400x300 monochrome (SSD1683 controller)
+
+  reg:
+    maxItems: 1
+
+  spi-max-frequency:
+    maximum: 20000000
+
+  reset-gpios:
+    maxItems: 1
+    description:
+      GPIO connected to the RSTB (reset) pin. Active low.
+
+  busy-gpios:
+    maxItems: 1
+    description:
+      GPIO connected to the BUSY pin. Active high when the controller is
+      busy updating the display.
+
+  dc-gpios:
+    maxItems: 1
+    description:
+      GPIO connected to the D/C (Data/Command) pin. Low for command, high
+      for data.
+
+  rotation:
+    enum: [0, 90, 180, 270]
+    description:
+      Display rotation in degrees counter clockwise (0,90,180,270)
+    $ref: /schemas/types.yaml#/definitions/uint32
+
+required:
+  - compatible
+  - reg
+  - reset-gpios
+  - busy-gpios
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        display@0 {
+            compatible = "gooddisplay,gdey042t81";
+            reg = <0>;
+            spi-max-frequency = <2000000>;
+            reset-gpios = <&gpio1 17 GPIO_ACTIVE_LOW>;
+            busy-gpios = <&gpio1 18 GPIO_ACTIVE_HIGH>;
+            dc-gpios = <&gpio1 19 GPIO_ACTIVE_HIGH>;
+        };
+    };
-- 
2.39.1