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Commit 14e85c0e authored by Alexandre Courbot's avatar Alexandre Courbot Committed by Linus Walleij
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gpio: remove gpio_descs global array 



Replace the ARCH_NR_GPIOS-sized static array of GPIO descriptors by
dynamically-allocated arrays for each GPIO chip.

This change makes gpio_to_desc() perform in O(n) (where n is the number
of GPIO chips registered) instead of O(1), however since n is rarely
bigger than 1 or 2 no noticeable performance issue is expected.
Besides this provides more incentive for GPIO consumers to move to the
gpiod interface. One could use a O(log(n)) structure to link the GPIO
chips together, but considering the low limit of n the hypothetical
performance benefit is probably not worth the added complexity.

This patch uses kcalloc() in gpiochip_add(), which removes the ability
to add a chip before kcalloc() can operate. I am not aware of such
cases, but if someone bisects up to this patch then I will be proven
wrong...

Signed-off-by: default avatarAlexandre Courbot <acourbot@nvidia.com>
Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
parent c8aaa1bf

drivers/gpio/gpiolib.c

+31 −16
Original line number Diff line number Diff line
@@ -47,8 +47,6 @@ 
 */

DEFINE_SPINLOCK(gpio_lock);



static struct gpio_desc gpio_desc[ARCH_NR_GPIOS];



#define GPIO_OFFSET_VALID(chip, offset) (offset >= 0 && offset < chip->ngpio)



static DEFINE_MUTEX(gpio_lookup_lock);
@@ -65,10 +63,22 @@ static inline void desc_set_label(struct gpio_desc *d, const char *label) 
 */

struct gpio_desc *gpio_to_desc(unsigned gpio)

{

	if (WARN(!gpio_is_valid(gpio), "invalid GPIO %d\n", gpio))

	struct gpio_chip *chip;

	unsigned long flags;



	spin_lock_irqsave(&gpio_lock, flags);



	list_for_each_entry(chip, &gpio_chips, list) {

		if (chip->base <= gpio && chip->base + chip->ngpio > gpio) {

			spin_unlock_irqrestore(&gpio_lock, flags);

			return &chip->desc[gpio - chip->base];

		}

	}



	spin_unlock_irqrestore(&gpio_lock, flags);



	WARN(1, "invalid GPIO %d\n", gpio);

	return NULL;

	else

		return &gpio_desc[gpio];

}

EXPORT_SYMBOL_GPL(gpio_to_desc);
@@ -91,7 +101,7 @@ struct gpio_desc *gpiochip_get_desc(struct gpio_chip *chip, 
 */

int desc_to_gpio(const struct gpio_desc *desc)

{

	return desc - &gpio_desc[0];

	return desc->chip->base + (desc - &desc->chip->desc[0]);

}

EXPORT_SYMBOL_GPL(desc_to_gpio);
@@ -206,7 +216,7 @@ static int gpiochip_add_to_list(struct gpio_chip *chip) 
/**

 * gpiochip_add() - register a gpio_chip

 * @chip: the chip to register, with chip->base initialized

 * Context: potentially before irqs or kmalloc will work

 * Context: potentially before irqs will work

 *

 * Returns a negative errno if the chip can't be registered, such as

 * because the chip->base is invalid or already associated with a
@@ -226,12 +236,11 @@ int gpiochip_add(struct gpio_chip *chip) 
	int		status = 0;

	unsigned	id;

	int		base = chip->base;

	struct gpio_desc *descs;



	if (base >= 0 &&

	    (!gpio_is_valid(base) || !gpio_is_valid(base + chip->ngpio - 1))) {

		status = -EINVAL;

		goto fail;

	}

	descs = kcalloc(chip->ngpio, sizeof(descs[0]), GFP_KERNEL);

	if (!descs)

		return -ENOMEM;



	spin_lock_irqsave(&gpio_lock, flags);
@@ -247,10 +256,8 @@ int gpiochip_add(struct gpio_chip *chip) 
	status = gpiochip_add_to_list(chip);



	if (status == 0) {

		chip->desc = &gpio_desc[chip->base];



		for (id = 0; id < chip->ngpio; id++) {

			struct gpio_desc *desc = &chip->desc[id];

			struct gpio_desc *desc = &descs[id];

			desc->chip = chip;



			/* REVISIT:  most hardware initializes GPIOs as
@@ -266,6 +273,8 @@ int gpiochip_add(struct gpio_chip *chip) 
		}

	}



	chip->desc = descs;



	spin_unlock_irqrestore(&gpio_lock, flags);



#ifdef CONFIG_PINCTRL
@@ -291,6 +300,9 @@ int gpiochip_add(struct gpio_chip *chip) 
unlock:

	spin_unlock_irqrestore(&gpio_lock, flags);

fail:

	kfree(descs);

	chip->desc = NULL;



	/* failures here can mean systems won't boot... */

	pr_err("%s: GPIOs %d..%d (%s) failed to register\n", __func__,

		chip->base, chip->base + chip->ngpio - 1,
@@ -331,6 +343,9 @@ void gpiochip_remove(struct gpio_chip *chip) 
	list_del(&chip->list);

	spin_unlock_irqrestore(&gpio_lock, flags);

	gpiochip_unexport(chip);



	kfree(chip->desc);

	chip->desc = NULL;

}

EXPORT_SYMBOL_GPL(gpiochip_remove);