[PATCH v2 1/2] leds: ncp5623: Add device tree binding documentation

[Florian Vaussard <florian.vaussard@gmail.com>]

Add device tree binding documentation for On Semiconductor NCP5623 I2C
LED driver. The driver can independently control the PWM of the 3
channels with 32 levels of intensity.

The current delivered by the current source can also be controlled. To
do so, the led-max-microamp property is used by each LED sub-node. The
maximum value is then found and used as a limit to compute the final
intensity of the current source. If a LED happens to have a lower limit,
the PWM is then used to limit the current to the requested value.

In order to control the current source, it is also necessary to know
the current on the Iref pin, hence the onnn,led-iref-microamp property.
It is usually set using an external bias resistor, following
Iref = Vref/Rbias with Vref=0.6V.

Signed-off-by: Florian Vaussard <florian.vaussard@heig-vd.ch>
---
 .../devicetree/bindings/leds/leds-ncp5623.txt      | 60 ++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/leds/leds-ncp5623.txt

diff --git a/Documentation/devicetree/bindings/leds/leds-ncp5623.txt b/Documentation/devicetree/bindings/leds/leds-ncp5623.txt
new file mode 100644
index 0000000..77dd7ad
--- /dev/null
+++ b/Documentation/devicetree/bindings/leds/leds-ncp5623.txt
@@ -0,0 +1,60 @@
+* ON Semiconductor - NCP5623 3-Channel LED Driver
+
+The NCP5623 is a 3-channel I2C LED driver. The brightness of each
+channel can be independently set using 32 levels. Each LED is represented
+as a sub-node of the device.
+
+Required properties:
+  - compatible: Should be "onnn,ncp5623"
+  - reg: I2C slave address (fixed to 0x38)
+  - #address-cells: must be 1
+  - #size-cells: must be 0
+  - onnn,led-iref-microamp: Current on the Iref pin in microampere. It depends
+    on the value of the external bias resistor Rbias, following
+    Iref = Vref / Rbias with Vref = 0.6V. This is used to set the intensity of
+    the current that can be provided by the internal current source, based on
+    the maximum current permitted by LED sub-nodes (see below), but no more than
+    Imax = 2400 * Iref.
+
+LED sub-nodes
+=============
+
+Required properties:
+  - reg : LED channel number (0..2)
+  - led-max-microamp: Maximum allowable current inside the LED in microampere.
+    This property is used to limit the PWM ratio, based on the intensity of the
+    internal current source (see above).
+
+Optional properties:
+  - label: Used for naming LEDs
+  - default-trigger: see Documentation/devicetree/bindings/leds/common.txt
+
+Example
+=======
+
+led1: ncp5623@38 {
+	#address-cells = <1>;
+	#size-cells = <0>;
+	compatible = "onnn,ncp5623";
+	reg = <0x38>;
+	onnn,led-iref-microamp = <10>;
+
+	led1r@0 {
+		label = "ncp:power:red";
+		linux,default-trigger = "default-on";
+		reg = <0>;
+		led-max-microamp = <20000>;
+	};
+
+	led1b@1 {
+		label = "ncp:power:blue";
+		reg = <1>;
+		led-max-microamp = <20000>;
+	};
+
+	led1g@2 {
+		label = "ncp:power:green";
+		reg = <2>;
+		led-max-microamp = <20000>;
+	};
+};
-- 
2.5.5