dt-bindings: leds: Add binding for spi-byte LED.

This patch adds the binding documentation for a simple SPI based LED
controller which use only one byte for setting the brightness.

Signed-off-by: Christian Mauderer <oss@c-mauderer.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>

diff --git a/Documentation/devicetree/bindings/leds/leds-spi-byte.txt b/Documentation/devicetree/bindings/leds/leds-spi-byte.txt
new file mode 100644 (file)
index 0000000..28b6b2d
--- /dev/null
+++ b/Documentation/devicetree/bindings/leds/leds-spi-byte.txt
@@ -0,0 +1,44 @@
+* Single Byte SPI LED Device Driver.
+
+The driver can be used for controllers with a very simple SPI protocol:
+- one LED is controlled by a single byte on MOSI
+- the value of the byte gives the brightness between two values (lowest to
+  highest)
+- no return value is necessary (no MISO signal)
+
+The value for lowest and highest brightness is dependent on the device and
+therefore on the compatible string.
+
+Depending on the compatible string some special functions (like hardware
+accelerated blinking) might can be supported too.
+
+The driver currently only supports one LED. The properties of the LED are
+configured in a sub-node in the device node.
+
+Required properties:
+- compatible: should be one of
+   * "ubnt,acb-spi-led"                microcontroller (SONiX 8F26E611LA) based device
+                               used for example in Ubiquiti airCube ISP
+
+Property rules described in Documentation/devicetree/bindings/spi/spi-bus.txt
+apply.
+
+LED sub-node properties:
+- label:
+       see Documentation/devicetree/bindings/leds/common.txt
+- default-state:
+       see Documentation/devicetree/bindings/leds/common.txt
+       Only "on" and "off" are supported.
+
+Example:
+
+led-controller@0 {
+       compatible = "ubnt,acb-spi-led";
+       reg = <0>;
+       spi-max-frequency = <100000>;
+
+       led {
+               label = "white:status";
+               default-state = "on";
+       };
+};