Documentation: dt-bindings: trickle charger dt binding document for ds1339

Some DS13XX devices have "trickle chargers". Introduce a device tree
binding for the resistor and diode configuration for enabling trickle
charger.

Signed-off-by: Matti Vaittinen <[e-mail]>
Acked-by: Jason Cooper <[e-mail]>
Cc: Rob Herring <[e-mail]>
Cc: Pawel Moll <[e-mail]>
Cc: Guenter Roeck <[e-mail]>
Cc: Alessandro Zummo <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Pavel Machek <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/devicetree/bindings/i2c/trivial-devices.txt

···
 cirrus,cs42l51		Cirrus Logic CS42L51 audio codec
 dallas,ds1307		64 x 8, Serial, I2C Real-Time Clock
 dallas,ds1338		I2C RTC with 56-Byte NV RAM
-dallas,ds1339		I2C Serial Real-Time Clock
 dallas,ds1340		I2C RTC with Trickle Charger
 dallas,ds1374		I2C, 32-Bit Binary Counter Watchdog RTC with Trickle Charger and Reset Input/Output
 dallas,ds1631		High-Precision Digital Thermometer

Documentation/devicetree/bindings/rtc/dallas,ds1339.txt

···
+* Dallas DS1339		I2C Serial Real-Time Clock
+
+Required properties:
+- compatible: Should contain "dallas,ds1339".
+- reg: I2C address for chip
+
+Optional properties:
+- trickle-resistor-ohms : Selected resistor for trickle charger
+	Values usable for ds1339 are 250, 2000, 4000
+	Should be given if trickle charger should be enabled
+- trickle-diode-disable : Do not use internal trickle charger diode
+	Should be given if internal trickle charger diode should be disabled
+Example:
+	ds1339: rtc@68 {
+		compatible = "dallas,ds1339";
+		trickle-resistor-ohms = <250>;
+		reg = <0x68>;
+	};