How to wake up an Android Embedded Board from Suspend by using a GPIO

Question

I am currently working on porting Android 4.4 (Kitkat) on an embedded system (Freescale i.MX6 based). In order to start my development, I used a few development kits (Wandboard, Boundary Device's BD-SL).

While working on the power management of my custom board, I had no trouble to put the devkits in suspend. However, I couldn't find how to wake them from sleep (other than power cycling them). The expected way of waking the system would be by getting an interrupt on a GPIO (e.g. the on-off button on an Android based phone).

I wanted to know what was the usual way to wake up an android device from suspend with a GPIO's interrupt. Though the question may seem trivial, I had trouble gathering all the information I needed from various searches on Google and specialized forums. I found a lot of information but nothing that covered the whole subject. Probably because I was missing the required background, I had trouble putting everything together without a code example. I guessed I was not the only one in this situation, thus this post.

Here are some of the information I found:

• Android PowerPanager and wake locks
• Android Power Management
• Android Power Management on i.MX6DQ/DL
• Android Input

Answer 1

In the end, I was digging too deep. The code example was right under my nose. Everything I needed was in the BD-SL devkit's board specific code (can be found in the BD-SL source tree in mydroid/BD-SL-i.MX6/kernel_imx/arch/arm/mach-mx6/board-mx6_nitrogen6x.c)

This code is specific to the Freescale i.MX6 provided kernel but the different parts should easily be ported/Adapted to other Android Embedded Platforms.

GPIO define. I am skipping the GPIO pin mux for simplicity. The pin needs to be multiplexed to the GPIO functionality:

#define GP_ONOFF_KEY        IMX_GPIO_NR(2, 3)

Definition of the input key

#define GPIO_BUTTON(gpio_num, ev_code, act_low, descr, wake)    \
{                               \
    .gpio       = gpio_num,             \
    .type       = EV_KEY,               \
    .code       = ev_code,              \
    .active_low = act_low,              \
    .desc       = "btn " descr,             \
    .wakeup     = wake,                 \
}

static struct gpio_keys_button buttons[] = {
    GPIO_BUTTON(GP_ONOFF_KEY, KEY_POWER, 1, "key-power", 1),
};

Definition of the corresponding platform data and platform device:

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

static struct platform_device button_device = {
    .name       = "gpio-keys",
    .id     = -1,
    .num_resources  = 0,
    .dev        = {
        .platform_data = &button_data,
    }
};

Registering of the platform device

static void __init add_device_buttons(void)
{
    platform_device_register(&button_device);
}

/*!
 * Board specific initialization.
 */
static void __init board_init(void)
{
    //...

    add_device_buttons();

    //...
}

And for completeness, the initialize data structure that points to the Board specific initialization

/*
 * initialize data structure.
 */
MACHINE_START(MX6_NITROGEN6X, "Boundary Devices Nitrogen6X/SABRE Lite Board")
    /* Maintainer: Boundary Devices */
    .boot_params = MX6_PHYS_OFFSET + 0x100,
    .fixup = fixup_mxc_board,
    .map_io = mx6_map_io,
    .init_irq = mx6_init_irq,
    .init_machine = board_init,
    .timer = &timer,
    .reserve = reserve,
MACHINE_END