Re: [PATCH 1/2] Input: Add binding document for a generic ADC keypad

[Jonathan Cameron <jic23@kernel.org>]

On 28/03/15 00:43, Andrew Bresticker wrote:
> Add a binding document for a generic ADC keypad.  Buttons on an ADC
> keypad are connected in a resistor ladder to an ADC.  The binding
> describes the mapping of ADC channel and voltage ranges to buttons.
> 
> Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
> Cc: Rob Herring <robh+dt@kernel.org>
> Cc: Pawel Moll <pawel.moll@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
> Cc: Kumar Gala <galak@codeaurora.org>

Just thinking about this, what options do we have for how such a keypad might
be wired.  The interesting cases are the more than one key at a time ones.

If that happens, then we end up with a voltage that should allow us to 
work out which combination of keys is pressed.

http://en.wikipedia.org/wiki/Resistor_ladder

The binding as it stands only works for single keys being pressed at a time
(I think!)

Do we want to make it flexible enough to cope with multiple keys?
I guess we'd need to model the common resistor ladder forms and provide
a way of specifying the different setups in the device tree.

J
> ---
>  .../devicetree/bindings/input/adc-keys.txt         | 43 ++++++++++++++++++++++
>  1 file changed, 43 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/input/adc-keys.txt
> 
> diff --git a/Documentation/devicetree/bindings/input/adc-keys.txt b/Documentation/devicetree/bindings/input/adc-keys.txt
> new file mode 100644
> index 0000000..c9a57de
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/input/adc-keys.txt
> @@ -0,0 +1,43 @@
> +Generic ADC keypad
> +==================
> +
> +Required properties:
> + - compatible: "adc-keys"
> + - poll-interval: Polling interval time in ms.
> + - io-channels: List of IIO channels used by the keypad.
> +   See ../iio/iio-bindings.txt for details.
> +
> +Optional properties:
> + - autorepeat: Enable auto-repeat.
> +
> +Each button on the ADC keypad is represented by a sub-node.
> +
> +Required sub-node properties:
> + - label: Descriptive name for the key.
> + - linux,code: Keycode to emit.
> + - channel: IIO channel (index into the 'io-channels' above) to which this
> +   button is attached.
> + - min-voltage: Minimum voltage in uV when this key is pressed.
> + - max-voltage: Maximum voltage in uV when this key is pressed.
> +
> +Optional sub-node properties:
> + - linux,input-type: Event type this key generates.  Defaults to 1 (EV_KEY) if
> +   not specified.
> +
> +Example:
> +
> +adc-keypad {
> +	compatible = "adc-keys";
> +	poll-interval = <100>;
> +	io-channels = <&adc 0>, <&adc 1>;
> +
> +	vol-up-button {
> +		label = "Volume Up";
> +		linux,code = <KEY_VOLUMEUP>;
> +		channel = <0>;
> +		min-voltage = <1600000>;
> +		max-voltage = <1640000>;
> +	};
> +
> +	...
> +};
>