[PATCH v3 02/14] dt-bindings: display: Add Solomon SSD16xx e-paper controller

[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 (as defined by panel-common, in degrees
counter clockwise) 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 [2] 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>
---
Changes in v3:
- Rename the file to solomon,ssd1683.yaml so that it matches an actual
  compatible string
- Drop the redundant "binding" from the subject
- Describe the compatible as oneOf/items from the start so that the next
  patch only adds a branch instead of rewriting these lines
- Reference panel/panel-common.yaml in allOf
- Add spi-3wire and document that omitting dc-gpios selects 3-wire mode
- Use the common 'rotation' property from panel-common instead of a local
  definition that said "clockwise"
- Remove rotation as it is already inherited by panel-common
- Set spi-3wire as true since supported by panel
---
 .../bindings/display/solomon,ssd1683.yaml     | 85 +++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/solomon,ssd1683.yaml

diff --git a/Documentation/devicetree/bindings/display/solomon,ssd1683.yaml b/Documentation/devicetree/bindings/display/solomon,ssd1683.yaml
new file mode 100644
index 000000000000..2e2aa195fb1e
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/solomon,ssd1683.yaml
@@ -0,0 +1,85 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/solomon,ssd1683.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Solomon Systech SSD16xx-based e-paper display panels
+
+maintainers:
+  - Devarsh Thakkar <devarsht@ti.com>
+
+description:
+  The SSD16xx family includes e-paper display controllers (SSD1673,
+  SSD1680, SSD1681, SSD1683, SSD1677) with integrated gate driver,
+  source driver and timing controller. Different panels use these
+  controllers in monochrome or 3-color (black/white/red) configurations.
+  The controller uses a 4-wire SPI interface and requires GPIO pins for
+  reset, busy status, and data/command control. A 3-wire mode is also
+  available where the D/C bit is transmitted along the SPI data line
+  before each byte.
+
+allOf:
+  - $ref: panel/panel-common.yaml#
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
+
+properties:
+  compatible:
+    oneOf:
+      - items:
+          - enum:
+              # Good Display 4.2" 400x300 monochrome e-paper panel
+              - gooddisplay,gdey042t81
+          - const: solomon,ssd1683
+
+  reg:
+    maxItems: 1
+
+  spi-max-frequency:
+    maximum: 20000000
+
+  spi-3wire: true
+
+  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. If omitted, the controller is driven in 3-wire
+      (9-bit) SPI mode, where the D/C bit is sent along the data line.
+
+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", "solomon,ssd1683";
+            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