How to use Keypad matrix on the ANDROID

Make sure that you have these products:

• ODROID-N2 or ODROID-C4
• Keypad Matrix
• Jumper Wires

For the wiring, you should wire a total number of cols and rows gpios.
You can choose empty GPIO like a pin 13 on the 40 pins.

keypad matrix use gpio matrix keypad driver. So to use the driver, you should make dtbo based on this driver.

https://github.com/hardkernel/linux/blob/odroidg12-4.9.y/Documentation/devicetree/bindings/input/matrix-keymap.txt

As you can see the document, you need two value. gpio key and input event code.

GPIO Key can be found above of the table.

You can find event code from here.

And, you should check 3 timing properties. debounce-delay-ms, col-scan-delay-us and col-switch-delay-ms.

first two properties are explained on the Documents.

col-switch-delay-ms is polling period property for keypad matrix.

Example dtbo file is already included to dtbs partition.keymatrix.dts

/dts-v1/;
/plugin/;

#include <dt-bindings/gpio/meson-g12a-gpio.h>
#include <dt-bindings/gpio/gpio.h>

/{
	fragment@0 {
		target-path = "/";

		__overlay__ {
			matrix_keypad: matrix-keypad {
				compatible = "gpio-matrix-keypad";
				col-gpios = <
					&gpio GPIOA_13 GPIO_ACTIVE_HIGH
					&gpio GPIOX_3 GPIO_ACTIVE_HIGH
					&gpio GPIOX_4 GPIO_ACTIVE_HIGH
					&gpio GPIOX_0 GPIO_ACTIVE_HIGH
					>;
				row-gpios = <
					&gpio GPIOX_1 GPIO_ACTIVE_HIGH
					&gpio GPIOX_2  GPIO_ACTIVE_HIGH
					&gpio GPIOX_14 GPIO_ACTIVE_HIGH
					&gpio GPIOX_15 GPIO_ACTIVE_HIGH
					>;
				/* sample keymap */
				linux,keymap = <
					0x00000074 /* row 0, col 0, KEY_POWER */
					0x00010052 /* row 0, col 1, KEY_KP0 */
					0x0002004f /* row 0, col 2, KEY_KP1 */
					0x00030050 /* row 0, col 3, KEY_KP2 */
					0x01000051 /* row 1, col 0, KEY_KP3 */
					0x0101004b /* row 1, col 1, KEY_KP4 */
					0x0102004c /* row 1, col 2, KEY_KP5 */
					0x0103004d /* row 1, col 3, KEY_KP6 */
					0x02000047 /* row 2, col 0, KEY_KP7 */
					0x02010048 /* row 2, col 1, KEY_KP8 */
					0x02020049 /* row 2, col 2, KEY_KP9 */
					>;
				gpio-activelow;
				debounce-delay-ms = <100>;
				col-scan-delay-us = <500>;
				col-switch-delay-ms = <20>;
				linux,no-autorepeat;
			};
		};
	};
};

You can find way to create customized dtbo file and way to apply from here