Documentation/devicetree/bindings/input/adc-keys.txt

   1 ADC attached resistor ladder buttons
   2 ------------------------------------
   3
   4 Required properties:
   5  - compatible: "adc-keys"
   6  - io-channels: Phandle to an ADC channel
   7  - io-channel-names = "buttons";
   8  - keyup-threshold-microvolt: Voltage above or equal to which all the keys are
   9                               considered up.
  10
  11 Optional properties:
  12         - poll-interval: Poll interval time in milliseconds
  13         - autorepeat: Boolean, Enable auto repeat feature of Linux input
  14           subsystem.
  15
  16 Each button (key) is represented as a sub-node of "adc-keys":
  17
  18 Required subnode-properties:
  19         - label: Descriptive name of the key.
  20         - linux,code: Keycode to emit.
  21         - press-threshold-microvolt: voltage above or equal to which this key is
  22                                      considered pressed.
  23
  24 No two values of press-threshold-microvolt may be the same.
  25 All values of press-threshold-microvolt must be less than
  26 keyup-threshold-microvolt.
  27
  28 Example:
  29
  30 #include <dt-bindings/input/input.h>
  31
  32         adc-keys {
  33                 compatible = "adc-keys";
  34                 io-channels = <&lradc 0>;
  35                 io-channel-names = "buttons";
  36                 keyup-threshold-microvolt = <2000000>;
  37
  38                 button-up {
  39                         label = "Volume Up";
  40                         linux,code = <KEY_VOLUMEUP>;
  41                         press-threshold-microvolt = <1500000>;
  42                 };
  43
  44                 button-down {
  45                         label = "Volume Down";
  46                         linux,code = <KEY_VOLUMEDOWN>;
  47                         press-threshold-microvolt = <1000000>;
  48                 };
  49
  50                 button-enter {
  51                         label = "Enter";
  52                         linux,code = <KEY_ENTER>;
  53                         press-threshold-microvolt = <500000>;
  54                 };
  55         };
  56
  57 +--------------------------------+------------------------+
  58 | 2.000.000 <= value             | no key pressed         |
  59 +--------------------------------+------------------------+
  60 | 1.500.000 <= value < 2.000.000 | KEY_VOLUMEUP pressed   |
  61 +--------------------------------+------------------------+
  62 | 1.000.000 <= value < 1.500.000 | KEY_VOLUMEDOWN pressed |
  63 +--------------------------------+------------------------+
  64 |   500.000 <= value < 1.000.000 | KEY_ENTER pressed      |
  65 +--------------------------------+------------------------+
  66 |              value <   500.000 | no key pressed         |
  67 +--------------------------------+------------------------+