Linux Driver APIs - gpio

Linux GPIO Library API

==================================
#include <linux/gpio.h>
*以下API如无特别提示，则默认返回值0代表执行成功，负值代表出错

0.Index
=======

- 1.GPIO Request
- 2.GPIO 输入输出设置
- 3.API for resource managed device
- 4.Debug GPIO
- 5.Sample Code

1.GPIO Request
==============
申请单个GPIO
-------------------

int gpio_request(unsigned gpio, const char *label)

e.g.

r = gpio_request(24, "gpio-24");
if (r < 0)
	return -EINVAL;

申请单个GPIO，同时配置该GPIO
---------------------------------------------

int gpio_request_one(unsigned gpio, unsigned long flags, const char *label)

e.g.

r = gpio_request_one(25, GPIOF_DIR_IN | GPIOF_INIT_HIGH, "my-gpio");
if (r < 0)
	return -EINVAL;

与gpio_request不同的是，gpio_request_one允许用户通过flag参数申请并设置GPIO。
flag可以是：gpio.h
GPIOF_OPEN_DRAIN
GPIOF_OPEN_SOURCE
GPIOF_DIR_IN
GPIOF_INIT_HIGH
GPIOF_EXPORT_CHANGEABLE

申请一组GPIO
-------------------

int gpio_request_array(const struct gpio *array, size_t num)

e.g.

const struct gpio[] = {
{
	.gpio = 26,
	.flag = 0,
	.label = "gpio-clk",
}, {
	.gpio = 27,
	.flag = GPIOF_OPEN_DRAIN,
	.label = "gpio-cc",
}
};
r = gpio_request_array(gpio, ARRAY_SIZE(gpio));
if (r < 0)
	return r;

对应的freeAPI
-------------------

void gpio_free(unsigned gpio)
gpio_free_array(const struct gpio *array, size_t num)

2.GPIO输入输出设置
==================
读取GPIO电平状态

int gpio_get_value(unsigned int gpio)

设置GPIO电平状态hi/lo

void gpio_set_value(unsigned int gpio, int value)

设置GPIO为输入态

int gpio_direction_input(unsigned gpio)

设置gpio为输出态，同时设置GPIO的电平状态

int gpio_direction_output(unsigned gpio, int value)

设置GPIO的去抖参数，debounce的单位是ms

int gpio_set_debounce(unsigned gpio, unsigned debounce)

GPIO number至IRQ number的转换

int gpio_to_irq(unsigned int gpio)

IRQ number至GPIO number的转换

int irq_to_gpio(unsigned int irq)

判断GPIO是否是有效的

bool gpio_is_valid(int number)

true - GPIO有效
flase - GPIO无效

3.API for resource managed device
=================================
使用这些API申请的GPIO不需要调用者free，当driver与device detach的时候，GPIO将被
自动free。调用者需要额外提供dev这个参数，除此以外，其他与以上描述的同名API用法一致。

int devm_gpio_request(struct device *dev, unsigned gpio, const char *label);
int devm_gpio_request_one(struct device *dev, unsigned gpio,
 unsigned long flags, const char *label);
void devm_gpio_free(struct device *dev, unsigned int gpio);

4.Debug GPIO
============
通过sysfs查看gpio状态
cat /sys/kernel/debug/gpio

5.Sample Code
============

#include <linux/gpio.h>
#include <linux/device.h>

#define GPIO_SCL 15
#define GPIO_SDA 16
#define GPIO_RESET 17
#define GPIO_IRQ 14

static int gpio_sample(struct device *dev)
{
	int r, irq;

	r = devm_gpio_request_one(dev,
		GPIO_SCL, GPIOF_INIT_HIGH, "scl");
	if (r < 0)
		return r;

	r = devm_gpio_request_one(dev,
		GPIO_SDA, GPIOF_INIT_HIGH, "sda");
	if (r < 0)
		return r;

	r = devm_gpio_request(dev, GPIO_RESET, "reset");
	if (r < 0)
		return r;
	gpio_direction_output(GPIO_RESET, 1);

	r = devm_gpio_request_one(dev, GPIO_IRQ,
		GPIOF_DRI_IN, "irq");
	if (r < 0)
		return r;

	irq = gpio_to_irq(GPIO_IRQ);
	printk("IRQ:%d", irq);

	// you can request_irq here.
	/* do hardware reset */
	gpio_set_value(GPIO_RESET, 0);
	udelay(10);
	gpio_set_value(GPIO_RESET, 1);

	return 0;
}