dt-bindings: iio: Add cros ec proximity yaml doc

Some cros ECs support a front proximity MKBP event via
'EC_MKBP_FRONT_PROXIMITY'. Add a DT binding to document this feature via
a node that is a child of the main cros_ec device node. Devices that
have this ability will describe this in firmware.

Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Benson Leung <bleung@chromium.org>
Cc: Guenter Roeck <groeck@chromium.org>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Gwendal Grignou <gwendal@chromium.org>
Cc: <devicetree@vger.kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20210211024601.1963379-3-swboyd@chromium.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/proximity/google,cros-ec-mkbp-proximity.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+
+$id: http://devicetree.org/schemas/iio/proximity/google,cros-ec-mkbp-proximity.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: ChromeOS EC MKBP Proximity Sensor
+
+maintainers:
+  - Stephen Boyd <swboyd@chromium.org>
+  - Benson Leung <bleung@chromium.org>
+  - Enric Balletbo i Serra <enric.balletbo@collabora.com>
+
+description: |
+  Google's ChromeOS EC sometimes has the ability to detect user proximity.
+  This is implemented on the EC as near/far logic and exposed to the OS
+  via an MKBP switch bit.
+
+properties:
+  compatible:
+    const: google,cros-ec-mkbp-proximity
+
+  label:
+    description: Name for proximity sensor
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    proximity {
+      compatible = "google,cros-ec-mkbp-proximity";
+      label = "proximity-wifi-lte";
+    };

Documentation/devicetree/bindings/mfd/google,cros-ec.yaml

@@ -94,6 +94,9 @@ properties:
   keyboard-controller:
     $ref: "/schemas/input/google,cros-ec-keyb.yaml#"
 
+  proximity:
+    $ref: "/schemas/iio/proximity/google,cros-ec-mkbp-proximity.yaml#"
+
   codecs:
     type: object
     additionalProperties: false
@@ -180,6 +183,10 @@ examples:
             interrupts = <99 0>;
             interrupt-parent = <&gpio7>;
             spi-max-frequency = <5000000>;
+
+            proximity {
+                    compatible = "google,cros-ec-mkbp-proximity";
+            };
         };
     };