EMC2305 (I2C)

This device is a RPM-based PWM Fan Speed Controller for up to 5 fans.

Each fan can beconfigured individually:

 - pwm-enable defines the PWM mode:
    0: PWM is disabled
    3: RPM based PWM

  - fan-div sets the fan divisor (for RPM mesaurement)
   1, 2 ,4 or 8

  - fan-target sets the target RPM speed (for RPM based PWM mode)
    max 16000 (according to data sheet)


1) The /emc2305 node

  Required properties:

   - compatible : must be "smsc,emc2305"
   - reg : I2C bus address of the device
   - #address-cells : must be <1>
   - #size-cells : must be <0>

  The node may contain child nodes for each fan that the platform uses.
  If no child nodes are given, all possible fan control channels are exposed.
  If at least one child node is given, only the configured fans are exposed.

  Example EMC2305 node:

    emc2305@2C {
	    compatible = "smsc,emc2305";
	    reg = <0x2C>;
	    #address-cells = <1>;
	    #size-cells = <0>;

	    [ child node definitions... ]
    }

2) fan nodes

  Required properties:

   - reg : the fan number (0 based)

  Optional properties:

   - fan-div : the fan divisor setting
   - fan-target : the fan target speed
   - pwm-enable : PWM mode

  Example EMC2305 fan node:

    fan@1 {
	    reg = <1>;
	    fan-div = <4>;
	    pwm-enable = <0>;
    };
