[PATCH v3 bus+gpio 2/5] dt-bindings: bus: Document moxtet bus binding

["Marek Behún" <marek.behun@nic.cz>]

This adds device tree binding documentation for the Moxtet bus, a bus
via which the different modules connected to the Turris Mox router can
be configured.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
---
 .../devicetree/bindings/bus/moxtet.txt        | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/bus/moxtet.txt

diff --git a/Documentation/devicetree/bindings/bus/moxtet.txt b/Documentation/devicetree/bindings/bus/moxtet.txt
new file mode 100644
index 000000000000..2bb998cbd3ad
--- /dev/null
+++ b/Documentation/devicetree/bindings/bus/moxtet.txt
@@ -0,0 +1,36 @@
+Turris Mox module configuration bus (over SPI)
+
+Required properties:
+ - compatible		: Should be "cznic,moxtet".
+ - #address-cells	: Has to be 1
+ - #size-cells		: Has to be 0
+ - spi-cpol		: Required inverted clock polarity
+ - spi-cpha		: Required shifted clock phase
+For other required and optional properties of SPI slave nodes please refer to
+../spi/spi-bus.txt.
+
+Required properties of subnodes:
+ - reg			: Should be position on the Moxtet bus
+
+The driver finds the devices connected to the bus by itself, but it may be
+needed to reference some of them from other parts of the device tree. In that
+case the devices can be defined as subnodes of the moxtet node.
+
+Example:
+
+	moxtet@1 {
+		#address-cells = <1>;
+		#size-cells = <0>;
+		compatible = "cznic,moxtet";
+		reg = <1>;
+		spi-max-frequency = <10000000>;
+		spi-cpol;
+		spi-cpha;
+
+		moxtet_sfp: gpio@0 {
+			compatible = "cznic,moxtet-sfp";
+			gpio-controller;
+			#gpio-cells = <2>;
+			reg = <0>;
+		}
+	};
-- 
2.19.2