dt-bindings: HID: i2c-hid: elan: Introduce Elan eKTH8D18

The Elan eKTH8D18 touchscreen controller is an I2C HID device with a
longer boot-up time. Power sequence timing wise it is compatible with
the eKTH6A12NAY, with a power-on delay of at least 5ms, 20ms
out-of-reset for I2C ack response, and 150ms out-of-reset for I2C HID
enumeration, both shorter than what the eKTH6A12NAY requires.
Enumeration and subsequent operation follows the I2C HID standard.

Add a compatible string for it with the ekth6a12nay one as a fallback.
No enum was used as it is rare to actually add new entries. These
chips are commonly completely backward compatible, and unless the
power sequencing delays change, there is no real effort being made to
keep track of new parts, which come out constantly.

Also drop the constraints on the I2C address since it's not really
part of the binding.

Reviewed-by: Douglas Anderson <[email protected]>
Reviewed-by: Rob Herring (Arm) <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
Signed-off-by: Chen-Yu Tsai <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Dmitry Torokhov <[email protected]>

Author: wens

Documentation/devicetree/bindings/input/elan,ekth6915.yaml

@@ -4,14 +4,14 @@
 $id: http://devicetree.org/schemas/input/elan,ekth6915.yaml#
 $schema: http://devicetree.org/meta-schemas/core.yaml#
 
-title: Elan eKTH6915 touchscreen controller
+title: Elan I2C-HID touchscreen controllers
 
 maintainers:
   - Douglas Anderson <[email protected]>
 
 description:
-  Supports the Elan eKTH6915 touchscreen controller.
-  This touchscreen controller uses the i2c-hid protocol with a reset GPIO.
+  Supports the Elan eKTH6915 and other I2C-HID touchscreen controllers.
+  These touchscreen controller use the i2c-hid protocol with a reset GPIO.
 
 allOf:
   - $ref: /schemas/input/touchscreen/touchscreen.yaml#
@@ -23,12 +23,14 @@ properties:
           - enum:
               - elan,ekth5015m
           - const: elan,ekth6915
+      - items:
+          - const: elan,ekth8d18
+          - const: elan,ekth6a12nay
       - enum:
           - elan,ekth6915
           - elan,ekth6a12nay
 
-  reg:
-    const: 0x10
+  reg: true
 
   interrupts:
     maxItems: 1