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GPIO操作在Linux系统上是常用功能,STM32MP1芯片平台也同样支持。从Linux 4.8版本开始,Linux引入了新的gpio操作方式,GPIO字符设备。不再使用以前SYSFS方式在"/sys/class/gpio"目录下来操作GPIO,而是,基于"文件描述符"的字符设备,每个GPIO组在"/dev"下有一个对应的gpiochip文件,例如"/dev/gpiochip0, /dev/gpiochip1"。使用常规的LInux文件操作方式即可操作这些gpiochip文件,基本可以概括为open() + ioctl() + poll() + read() + close()。


STM32MP1平台的gpiochip文件描述

字符设备描述
/dev/gpiochip0GPIOA
/dev/gpiochip1GPIOB
/dev/gpiochip2GPIOC
/dev/gpiochip3GPIOD
/dev/gpiochip4GPIOE
/dev/gpiochip5GPIOF
/dev/gpiochip6GPIOG
/dev/gpiochip7GPIOH
/dev/gpiochip8GPIOI
/dev/gpiochip9GPIOJ
/dev/gpiochip10GPIOK
/dev/gpiochip11GPIOZ


gpiochip 操作

gpio申请

flags: desired flags for the desired GPIO lines, such as GPIOHANDLE_REQUEST_OUTPUT, GPIOHANDLE_REQUEST_ACTIVE_LOW etc, OR:ed * together. Note that even if multiple lines are requested, the same flags * must be applicable to all of them, if you want lines with individual * flags set, request them one by one. It is possible to select * a batch of input or output lines, but they must all have the same * characteristics, i.e. all inputs or all outputs, all active low etc

lines: number of lines requested in this request, i.e. the number of valid fields in the above arrays, set to 1 to request a single line

struct gpiohandle_request {
	__u32 lineoffsets[GPIOHANDLES_MAX];
	__u32 flags;
	__u8 default_values[GPIOHANDLES_MAX];
	char consumer_label[32];
	__u32 lines;
	int fd;
};

#define GPIOHANDLES_MAX 64
#define GPIOHANDLE_REQUEST_INPUT (1UL << 0)
#define GPIOHANDLE_REQUEST_OUTPUT (1UL << 1)
#define GPIOHANDLE_REQUEST_ACTIVE_LOW (1UL << 2)
#define GPIOHANDLE_REQUEST_OPEN_DRAIN (1UL << 3)
#define GPIOHANDLE_REQUEST_OPEN_SOURCE (1UL << 4)

gpio 操作数据

struct gpiohandle_data {
	__u8 values[GPIOHANDLES_MAX];
};


gpio event的申请

handleflags: desired handle flags for the desired GPIO line, such as GPIOHANDLE_REQUEST_ACTIVE_LOW or GPIOHANDLE_REQUEST_OPEN_DRAIN

eventflags: desired flags for the desired GPIO event line, such as GPIOEVENT_REQUEST_RISING_EDGE or GPIOEVENT_REQUEST_FALLING_EDGE

struct gpioevent_request {
	__u32 lineoffset;
	__u32 handleflags;
	__u32 eventflags;
	char consumer_label[32];
	int fd;
};
#define GPIOEVENT_REQUEST_RISING_EDGE (1UL << 0)
#define GPIOEVENT_REQUEST_FALLING_EDGE (1UL << 1)
#define GPIOEVENT_REQUEST_BOTH_EDGES ((1UL << 0) | (1UL << 1))

gpio event

struct gpioevent_data {
        __u64 timestamp;
        __u32 id;
};
#define GPIOEVENT_EVENT_RISING_EDGE 0x01
#define GPIOEVENT_EVENT_FALLING_EDGE 0x02



以下是使用C语言操作PZ0管脚的示例代码。

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <unistd.h>

#include <linux/gpio.h>

int main(int argc, char **argv)
{
struct gpiohandle_request req;
struct gpiohandle_data data;
char chrdev_name[20];
int fd, ret;

strcpy(chrdev_name, "/dev/gpiochip11");

/* Open device: gpiochip11 for GPIO bank Z */
fd = open(chrdev_name, 0);
if (fd == -1) {
ret = -errno;
fprintf(stderr, "Failed to open %s\n", chrdev_name);

return ret;
}

/* request GPIO line: GPIO_Z_0 */
req.lineoffsets[0] = 0;
req.flags = GPIOHANDLE_REQUEST_OUTPUT;
memcpy(req.default_values, &data, sizeof(req.default_values));
strcpy(req.consumer_label, "led_gpio_z_0");
req.lines = 1;

ret = ioctl(fd, GPIO_GET_LINEHANDLE_IOCTL, &req);
if (ret == -1) {
ret = -errno;
fprintf(stderr, "Failed to issue GET LINEHANDLE IOCTL (%d)\n",
ret);
}
if (close(fd) == -1)
perror("Failed to close GPIO character device file");

/* Start led blinking */
while(1) {

data.values[0] = !data.values[0];
ret = ioctl(req.fd, GPIOHANDLE_SET_LINE_VALUES_IOCTL, &data);
if (ret == -1) {
ret = -errno;
fprintf(stderr, "Failed to issue %s (%d)\n",
"GPIOHANDLE_SET_LINE_VALUES_IOCTL", ret);
}
sleep(1);
}

/* release line */
ret = close(req.fd);
if (ret == -1) {
perror("Failed to close GPIO LINEHANDLE device file");
ret = -errno;
}
return ret;
}

将以上代码保存为gpio.c文件,然后加载SDK环境变量后,就可以编译了。

$CC gpio.c -o gpio

编译后的gpio文件,可以拷贝到开发板上运行。

Libgpiod

由于gpiochip的方式,基于C语言,所以开发者实现了Libgpiod,提供了一些工具和更简易的C API接口。

Libgpiod (Library General Purpose Input/Output device)  提供了完整的API 给开发者,同时还提供了一些用户空间下的应用来操作GPIO。

  • gpiodetect – list all gpiochips present on the system, their names, labels and number of GPIO lines
  • gpioinfo – list all lines of specified gpiochips, their names, consumers, direction, active state and additional flags
  • gpioget – read values of specified GPIO lines
  • gpioset – set values of specified GPIO lines, potentially keep the lines exported and wait until timeout, user input or signal
  • gpiofind – find the gpiochip name and line offset given the line name
  • gpiomon – wait for events on GPIO lines, specify which events to watch, how many events to process before exiting or if the events should be reported to the console

仓库地址 https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/

 API https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/tree/include/gpiod.h

libgpiod introduction video: https://www.youtube.com/watch?v=76j3TIqTPTI


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