最近用到gpio中断，gpio中断也是嵌入式系统用的比较多的。

对于GPIO操作 linux 有一套标准的 API，set value、get value之类的，当然也有关于中断的。

关于中断的就是：

static inline int gpio_to_irq(unsigned int gpio)

{

return __gpio_to_irq(gpio);

}

1 使用gpio中断

在linux模块中使用gpio中断的步骤通常如下

1)实现中断处理函数。

static irqreturn_t myIntHandler(int irq, void *dev_id)

{

printk("Interrupt IN\n");

return IRQ_HANDLED

}

2)初始化函数

int xxx_init()

{

int ret, irqno;

ret = gpio_request(gpioNo, "mygpiopin");

if(ret){

printk("irq pin request io failed.\n");

return -1;

}

irqno= gpio_to_irq(gpioNo);

ret = request_irq(irqno,myIntHandler , RQF_TRIGGER_RISING|IRQF_TRIGGER_FALLING, "myinterrupt", NULL);

if(ret) {

printk(KERN_ERR "can not get irq\n");

return ret;

}

}就两个函数：

gpio_request  通常用来检测这个gpio是否可用，是否已经在使用了。

gpio_to_irq 转换gpio编号到对应irq号。

之后就是熟悉的request_irq

有时候还会加一个gpio_is_valid，判断一下gpioNo是否合理，通常自己察看芯片手册填入正确gpio number，不需要再再在这里判断一下。

2,gpio中断API的实现过程

简单看一下。

int gpio_request(unsigned gpio, const char *label)

{

return gpiod_request(gpio_to_desc(gpio), label);

}

先看参数

gpio_to_desc(gpio)

都在gpiolib.c中

static struct gpio_desc *gpio_to_desc(unsigned gpio)

{

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

return NULL;

else

return &gpio_desc[gpio];

}

这里有个全局的数组，看样子是每一个gpio都在这个数组里有这么一项，这个结构体如下

struct gpio_desc {

struct gpio_chip*chip;

unsigned longflags;

/* flag symbols are bit numbers */

#define FLAG_REQUESTED0

#define FLAG_IS_OUT1

#define FLAG_EXPORT2/* protected by sysfs_lock */

#define FLAG_SYSFS3/* exported via /sys/class/gpio/control */

#define FLAG_TRIG_FALL4/* trigger on falling edge */

#define FLAG_TRIG_RISE5/* trigger on rising edge */

#define FLAG_ACTIVE_LOW6/* sysfs value has active low */

#define FLAG_OPEN_DRAIN7/* Gpio is open drain type */

#define FLAG_OPEN_SOURCE 8/* Gpio is open source type */

#define ID_SHIFT16/* add new flags before this one */

#define GPIO_FLAGS_MASK((1 << ID_SHIFT) - 1)

#define GPIO_TRIGGER_MASK(BIT(FLAG_TRIG_FALL) | BIT(FLAG_TRIG_RISE))

#ifdef CONFIG_DEBUG_FS

const char*label;

#endif

};主要就是有个 struct gpio_chip类型的指针

回到gpiod_request，其他代码先忽略，主要就两句，就是我加注释的地方

static int gpiod_request(struct gpio_desc *desc, const char *label)

{

struct gpio_chip*chip;

intstatus = -EPROBE_DEFER;

unsigned longflags;

if (!desc) {

pr_warn("%s: invalid GPIO\n", __func__);

return -EINVAL;

}

spin_lock_irqsave(&gpio_lock, flags);

chip = desc->chip;//取得desc中的struct gpio_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_hwgpio(desc));//调用desc[gpio]-〉chip-〉request

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);

gpiod_get_direction(desc);

spin_lock_irqsave(&gpio_lock, flags);

}

done:

if (status)

pr_debug("_gpio_request: gpio-%d (%s) status %d\n",

desc_to_gpio(desc), label ? : "?", status);

spin_unlock_irqrestore(&gpio_lock, flags);

return status;

}

chip-〉request有两个参数，一个是chip另一个是

/*

* Return the GPIO number of the passed descriptor relative to its chip

*/

static int gpio_chip_hwgpio(const struct gpio_desc *desc)

{

return desc - &desc->chip->desc[0];

}

看注释也很清楚，gpio号相对于它的chip的偏移。 看来这个struct gpio_chip非常重要，看看这个chip是在哪里赋值到gpio_desc[]这个数组的。

/**

* gpiochip_add() - register a gpio_chip

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

* Context: potentially before irqs or kmalloc 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

* different chip. Otherwise it returns zero as a success code.

*

* When gpiochip_add() is called very early during boot, so that GPIOs

* can be freely used, the chip->dev device must be registered before

* the gpio framework's arch_initcall(). Otherwise sysfs initialization

* for GPIOs will fail rudely.

*

* If chip->base is negative, this requests dynamic assignment of

* a range of valid GPIOs.

*/

int gpiochip_add(struct gpio_chip *chip)

{

..........略

if (status == 0) {

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

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

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

desc->chip = chip;

/* REVISIT: most hardware initializes GPIOs as

* inputs (often with pullups enabled) so power

* usage is minimized. Linux code should set the

* gpio direction first thing; but until it does,

* and in case chip->get_direction is not set,

* we may expose the wrong direction in sysfs.

*/

desc->flags = !chip->direction_input

? (1 << FLAG_IS_OUT)

: 0;

}

}

..............略

}

在这个函数里面全局数组gpio_desc被一一赋值了。

而这个gpiochip_add会在底层芯片厂商各自的gpio初始化函数里调用。 位置通常在各厂商各自的gpio-xxx.c

struct gpio_chip也会在那里定义，通常与硬件寄存器相关，不做分析。

gpio_request完了，还有gpio_to_irq,其实是一样的，还是最终会调用，stuct gpio_chip中的to_irq。

反过来说bsp的编写者，初始化之后，只要实现stuct gpio_chip 再调用gpiochip_add,gpio的API就可以供用户使用了。