I.MX6 bq27441 GPOUT interrupt

/********************************************************************
 *                  I.MX6 bq27441 GPOUT interrupt
 * 说明：
 *     由于目前的bq27441驱动中没有GPOUT中断驱动，所以需要另外加上，其
 * 中有参考TI的驱动，但是内核版本不一致，所以处理方式也不一致。
 *
 *                                  2016-7-15 深圳 南山平山村 曾剑锋
 *******************************************************************/

一、参考文档：
    a reasonable example of a work queue?
        http://www.spinics.net/lists/newbies/msg27303.html

二、修改drivers/power/bq27x00_battery.c
    ......
    #include <linux/interrupt.h>
    #include <linux/gpio.h>
    
    #define SABRESD_UAUGE_PIN        IMX_GPIO_NR(1, 29)

    ......

    static void battery_irq(struct work_struct *unused);
    static DECLARE_DELAYED_WORK(battery_irq_work, battery_irq);
    struct bq27x00_device_info *battery_irq_work_di = NULL;

    static void battery_irq(struct work_struct *unused)
    {
        if (battery_irq_work_di != NULL) 
            bq27x00_update(battery_irq_work_di);
    }

    static irqreturn_t bq27xxx_battery_irq_handler_thread(int irq, void *data)
    {
        struct bq27x00_device_info *di = data;
        battery_irq_work_di = di;

        schedule_delayed_work(&battery_irq_work, 0);

        return IRQ_HANDLED;
    }

    ......

    static int __init bq27x00_battery_probe(struct i2c_client *client,
                     const struct i2c_device_id *id)
    {
        ......
        gpio_request(SABRESD_UAUGE_PIN, "sabresd_uauge_pin");
        gpio_direction_input(SABRESD_UAUGE_PIN);
        unsigned int irq = gpio_to_irq(SABRESD_UAUGE_PIN);
        int ret = request_irq(irq, bq27xxx_battery_irq_handler_thread,
                IRQF_TRIGGER_RISING,
                 "sabresd_uauge_pin", di);
        enable_irq_wake(irq);
        ......
    }