Linux下GPIO驅動（四） ----gpio_request();gpio_free();

//gpio_request申請gpio口

int gpio_request(unsigned gpio, const char *label)
{
    struct gpio_desc    *desc;
    struct gpio_chip    *chip;
    int            status = -EINVAL;
    unsigned long        flags;

    spin_lock_irqsave(&gpio_lock, flags); // gpio_lock是自旋鎖，上鎖，保存FLAG在flags變量
    if (!gpio_is_valid(gpio))
        goto done;
    desc = &gpio_desc[gpio];
    chip = desc->chip;
    if (chip == NULL)
        goto done;

    if (!try_module_get(chip->owner)) // 該函數用於增加模塊使用計數；若返回為0，表示調用失敗，希望使用的模塊沒有被加載或正在被卸載中       goto done;

    /* NOTE:  gpio_request() can be called in early boot,
     * before IRQs are enabled, for non-sleeping (SOC) GPIOs.
     */

    if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) { // 原子操作，將flags的第FLAG_REQUESTED位置1,並返回其原值        
    desc_set_label(desc, label ? : "?");// 如果原來的值是0, 執行desc_set_label, 對desc->chip.label賦值，如果label有定義，直接用定義，比如上面的“temporary”，否則用“？”      
    status = 0;
    } else {
        status = -EBUSY;
        module_put(chip->owner); // 該函數用於減少模塊使用計數goto done;
    }

    if (chip->request) {// chip->request在linux初始化時是沒有指向的       /* chip->request may sleep */
        spin_unlock_irqrestore(&gpio_lock, flags);// 如果chip->request不為0, 解鎖，因為后面調用的chip->request有可能睡眠       
        status = chip->request(chip, gpio - chip->base);
        spin_lock_irqsave(&gpio_lock, flags);

        if (status < 0) {
            desc_set_label(desc, NULL);
            module_put(chip->owner);
            clear_bit(FLAG_REQUESTED, &desc->flags);
        }
    }

done:
    if (status)
        pr_debug("gpio_request: gpio-%d (%s) status %d\n",
            gpio, label ? : "?", status);
    spin_unlock_irqrestore(&gpio_lock, flags);
    return status;
}
EXPORT_SYMBOL_GPL(gpio_request);

void gpio_free(unsigned gpio)
{
    unsigned long        flags;
    struct gpio_desc    *desc;
    struct gpio_chip    *chip;

    might_sleep();

    if (!gpio_is_valid(gpio)) {
        WARN_ON(extra_checks);
        return;
    }

    gpio_unexport(gpio);

    spin_lock_irqsave(&gpio_lock, flags);

    desc = &gpio_desc[gpio];
    chip = desc->chip;
    if (chip && test_bit(FLAG_REQUESTED, &desc->flags)) {
        if (chip->free) {
            spin_unlock_irqrestore(&gpio_lock, flags);
            might_sleep_if(extra_checks && chip->can_sleep);
            chip->free(chip, gpio - chip->base);
            spin_lock_irqsave(&gpio_lock, flags);
        }
        desc_set_label(desc, NULL);
        module_put(desc->chip->owner);
        clear_bit(FLAG_ACTIVE_LOW, &desc->flags);
        clear_bit(FLAG_REQUESTED, &desc->flags);
    } else
        WARN_ON(extra_checks);

    spin_unlock_irqrestore(&gpio_lock, flags);
}
EXPORT_SYMBOL_GPL(gpio_free);