GPIO keys

Introduction

How to use gpio-keys driver to read states of the user switch of your Armadeus board. Your APF51|APF27|APF28 development board feature a user switch connected to a GPIO pin. The driver gpio-keys translates GPIO events in key/button events. Here are the GPIO used for the user button/switch for each APF board:

• APF27: GPIO_PORTF | 13
• APF28: PINID_GPMI_CE1N (Bank 0 - bit 17)
• APF51: GPIO1_3

Configuration

First, you need to enable the gpio_keys in your kernel.

Device Drivers  --->
     Input device support  --->
           <*>   Event interface
           [*]   Keyboards  --->
               <*>   GPIO Buttons

Without device tree

Then, in your apfXX-dev.c, you would need to define your GPIO button before the variable platform_devices[] and also include gpio_keys.h and input.h. his code is already implemented for the APF27, APF28 and APF51 so the source code hereafter (for the APF27) is only present as a reference sample to understand how to activate a GPIO KEY driver.

#include <linux/gpio_keys.h>
#include <linux/input.h>

/* GPIO KEYS */
#if defined(CONFIG_KEYBOARD_GPIO) || defined(CONFIG_KEYBOARD_GPIO_MODULE)
static struct gpio_keys_button apf27dev_gpio_keys[] = {
	{
		.code = BTN_EXTRA, /* See include/linux/input.h */
		.gpio = (GPIO_PORTF | 13), /* GPIO number */
		.active_low = 1,
		.desc = "s1", /* Button description*/
		.wakeup = 0,
	},
};

static struct gpio_keys_platform_data apf27dev_gpio_keys_data = {
	.buttons = apf27dev_gpio_keys,
	.nbuttons = ARRAY_SIZE(apf27dev_gpio_keys),
};

static struct platform_device apf27dev_gpio_keys_device = {
	.name = "gpio-keys",
	.id = -1,
	.dev = {
		.platform_data = &apf27dev_gpio_keys_data,
	},
};
#endif /* CONFIG_KEYBOARD_GPIO */

Add the button to get it recognized by the card.

static struct platform_device *platform_devices[] __initdata = {
#if defined(CONFIG_KEYBOARD_GPIO) || defined(CONFIG_KEYBOARD_GPIO_MODULE)
	&apf27dev_gpio_keys_device,
#endif
	ALSA_SOUND
};

With device tree

This description is based to the APF28dev board and the modifications must be done into buildroot/output/build/linux-xxx/arch/arm/boot/dts/imx28-apf28dev.dts.

To define gpio-keys, you need to add a node and a sub-node after all peripheral nodes :

gpio-keys {
        compatible = "gpio-keys";

        left-key {
            label = "Left key";
            gpios = <&gpio1 18 0>;
            linux,code = <69>; /* KEY_LEFT */
        };
    }

It is possible to add as many node you want (within the limits of available pins).

A key node contains :

* a name (left-key)
* a label 
* a gpio <&gpioX Y 0> with X is the bank number and Y the pin number
* a linux code, available in buildroot/output/build/linux-xxx/include/uapi/linux/input.h

For each key, you need to add the corresponding GPIO in hog sub-node of pinctrl node

hog_pins_apf28dev: hog@0 {
                    ...
                    fsl,pinmux-ids = <
                        ...
                        0x1123 /* MX28_PAD_LCD_D18__GPIO_1_18 */
                        ...
                    >;
                    ...
                };

The pinmux is available in buildroot/output/build/linux-xxx/Documentation/devicetree/bindings/pinctrl/fsl,mxs-pinctrl.txt

Usage

# cat /dev/input/event0

Then you should see weirds characters when pressing the user button of the apf51_dev board:

 T
 ����T
      �T
        �
         ��T
            %�

• if the test wiped out your console, you can get it back with:

# reset

You also can use the tool evtest.

Hardware handling  --->
     [*] input-tools
          [*]   evtest

 # evtest /dev/input/event0
...
Event: time 1335981358.550329, type 22 (EV_PWR), code 0 (), value 1
Event: time 1335981358.550330, -------------- SYN_REPORT ------------
Event: time 1335981358.550329, type 22 (EV_PWR), code 0 (), value 0
Event: time 1335981358.550330, -------------- SYN_REPORT ------------

Links

http://www.kernel.org/doc/Documentation/input/