Linux driver GPIO ownership

gpio_request() : Use test and set to verify GPIO and get ownership
gpio_free() : Release ownership
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int gpio_request(unsigned gpio, const char *label)

{

    struct gpio_desc    *desc;

    struct gpio_chip    *chip;

    int         status = -EPROBE_DEFER;

    unsigned long       flags;

    spin_lock_irqsave(&gpio_lock, flags);

    if (!gpio_is_valid(gpio)) {

        status = -EINVAL;

        goto done;

    }

    desc = &gpio_desc[gpio];

    chip = desc->chip;

    if (chip == NULL)

        goto done;

    if (!try_module_get(chip->owner))

        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) {

        desc_set_label(desc, label ? : "?");

        status = 0;

    } else {

        status = -EBUSY;

        module_put(chip->owner);

        goto done;

    }

    if (chip->request) {

        /* chip->request may sleep */

        spin_unlock_irqrestore(&gpio_lock, flags);

        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);

            goto done;

        }

    }

    if (chip->get_direction) {

        /* chip->get_direction may sleep */

        spin_unlock_irqrestore(&gpio_lock, flags);

        gpio_get_direction(gpio);

        spin_lock_irqsave(&gpio_lock, 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);




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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);

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Refer to:

1. https://e2e.ti.com/support/embedded/linux/f/354/t/390011

2. http://clhjoe.blogspot.tw/2012/07/gpio.html

3. http://bluequiet.blogspot.tw/2010/12/driver.html

4. https://chromium.googlesource.com/chromiumos/third_party/kernel-next/+/chromeos-3.18-test/drivers/gpio/gpiolib.c
5. http://www.cnblogs.com/hello2mhb/p/3279322.html