基于Amlogic 安卓9.0, 驱动简说（五）：基于GPIO、LED子系统的LED驱动

一、篇头

• 本章介绍LED子系统的使用。
• 使用LED子系统，可以轻松实现对LED，例如常见的闪烁和亮度控制功能。
• 简单起见，本章先使用GPIO实现，在不模拟PWM的情况下，只能实现点亮和灭灯的效果，重点是介绍GPIO、LED子系统的使用。

本文基于Amlogic T972 ， Android 9.0， 内核版本 4.9.113

二、系列文章

第1篇：基于Amlogic 安卓9.0, 驱动简说（一）：字符设备驱动，手动创建设备
第2篇：基于Amlogic 安卓9.0, 驱动简说（二）：字符设备驱动，自动创建设备
第3篇：基于Amlogic 安卓9.0, 驱动简说（三）：使用misc框架，让驱动更简单
第4篇：基于Amlogic 安卓9.0, 驱动简说（四）：Platform平台驱动，驱动与设备的分离
第5篇：基于Amlogic 安卓9.0, 驱动简说（五）：基于GPIO、LED子系统的LED驱动

三、准备工作

3.1 原理图：挑选测试用GPIO脚

（1） 红色LED: GPIOZ_6
（2） 绿色LED: GPIOZ_2
（3） 黄色LED: GPIOZ_1
（4） GND接地

3.2 LED模块

• 如下4个PIN脚，分别连接至开发板的4个引脚

四、源码解析

4.1 DTS设备树

    aml_led_class{
   
   
        status = "okay";
        compatible = "szhou,aml_led_class";
        /*
        *     (1) amlled-gpios 是使用新版GPIO子系统API的固定写法，必须以 -gpios 结尾
        *     (2) “&gpio” : 引用的GPIO控制器的名称
        *     (3) “GPIOZ_X ” :是一个宏定义，可转换成具体的gpio index
        *     (4) 最后的GPIO_ACTIVE_HIGH，代表此PIN脚物理上是高电平有效
        */
        amlled-gpios =  <&gpio GPIOZ_6 GPIO_ACTIVE_HIGH>,  //red_led
                        <&gpio GPIOZ_2 GPIO_ACTIVE_HIGH>,  //green_led
                        <&gpio GPIOZ_1 GPIO_ACTIVE_HIGH>;  //yellow_led
    };

4.2 驱动源码

如下是驱动源码，已添加详细解释

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/platform_device.h>
#include <linux/io.h>
#include <linux/of.h>
#include <linux/leds.h> /* 包含 struct led_classdev 结构体，及API*/
#include <linux/gpio/consumer.h> /* 包含新版本GPIO子系统： -gpiod- API*/


/*
*
 私有结构体,  可自行增加所需成员, 但必须包含 struct led_classdev
*/
struct led_dev
{
   
   
    struct led_classdev cdev;
    struct gpio_desc *desc;
};

static char *name_red = "red";
static char *name_green = "green";
static char *name_yellow = "yellow";
static struct led_dev *led_device[3];




/* 
* （1）对 /sys/class/leds/red/brightness 等LED属性进行控制时，会回调此函数 
*/
static void led_control(struct led_classdev *led_cdev, enum led_brightness brightness)
{
   
   
    struct led_dev *led = container_of(led_cdev, struct led_dev, cdev);

    pr_info(" ENTER led_control  led(0x%p)->desc=0x%p \n", led, led->desc);    

    //根据设定，设置亮或灭
    if (brightness != LED_OFF) {
   
    
        gpiod_set_value(led->desc , 1);
        pr_info(" gpiod_set_value(led->desc , 1) \n");        

    }else{
   
   

        gpiod_set_value(led->desc , 0);
        pr_info(" gpiod_set_value(led->desc , 0) \n");        
    }

    pr_info("EXIT led_control \n");
}

/*
* （1）在检测到DT中.compatible = "szhou,aml_led_class"的节点后，会自动调用此函数，实现初始化
*/
static int __init ledclass_plat_probe(struct platform_device *pdev)
{
   
   

    struct device *dev = &pdev->dev;
    int i, count, ret;

    pr_info( "ledclass_plat_probe enter\n");

    /* 获取amlled-gpios里面gpio的数量 */
    count = gpiod_count(dev, "amlled");
    if (count ==  -ENOENT)
        return -ENOENT;

    dev_info(dev, "gpiod_count = %d \n", count);

    /* 填充每个gpio-led对象，并注册到LED子系统 */
    for(i=0; i<count; i++){
   
   

        //struct led_dev *led_device;
        //struct gpio_desc *desc = NULL;

        led_device[i] = devm_kzalloc(dev, sizeof(struct led_dev), GFP_KERNEL);
        if (!led_device[i])
            return -ENOMEM;

        /* 申请并初始化gpio描述符，电平初始化为GPIOD_OUT_LOW，即设为输出脚、低电平 */
        led_device[i]->desc = gpiod_get_index(dev, "amlled", i, GPIOD_OUT_LOW);
        pr_info(" ledclass_plat_probe  led(0x%p)->desc=0x%p \n", led_device[i], led_device[i]->desc);    

        switch(i){
   
   

            case 0:
                led_device[0]->cdev.name = name_red;
                pr_info("zs, 000000000   \n");
                //led_device->cdev.default_trigger = "heartbeat";//红灯将使用默认的闪烁程序，若启用，则要添加类似互斥锁
                break;
            case 1:
                led_device[1]->cdev.name = name_green;
                pr_info("zs, 111111111111111   \n");                
                break;
            case 2:
                led_device[2]->cdev.name = name_yellow;
                pr_info("zs, 22222222222   \n");                
                break;    
            default:
                pr_info( "zs, i=%d, default \n", i);

        }

        pr_info("zs, 33333333333333   \n");    

        /* 初始化亮度值，以及LED的控制函数 */
        led_device[i]->cdev.brightness = LED_OFF;
        led_device[i]->cdev.brightness_set = led_control;

        /* 注册到LED子系统 */
        ret = devm_led_classdev_register(dev, &led_device[i]->cdev);
        pr_info( "zs, platform_probe  devm_led_classdev_register [%d], cdev->name=%s \n", i,  led_device[i]->cdev.name);
        if (ret) {
   
   
            dev_err(dev, "failed to register the led %s\n", led_device[i]->cdev.name);
            return ret;
        }

    }

    dev_info(dev, "ledclass_plat_probe exit\n");
    return 0;
}

static int __exit ledclass_plat_remove(struct platform_device *pdev)
{
   
   
    int i=0;
    dev_info(&pdev->dev, "ledclass_plat_remove enter\n");

    for(i=0; i<3; i++)
    {
   
    
        gpiod_put(led_device[i]->desc);  //释放GPIO描述符      
    }

    dev_info(&pdev->dev, "ledclass_plat_remove exit\n");
    return 0;
}


/*
* 设备树的匹配属性 .compatible ，需完全相同才会匹配
*/
static const struct of_device_id my_of_ids[] = {
   
   
    {
   
    .compatible = "szhou,aml_led_class"},
    {
   
   },
};

MODULE_DEVICE_TABLE(of, my_of_ids);


/*
* led_platform_driver 结构体
*/
static struct platform_driver led_platform_driver = {
   
   
    .probe = ledclass_plat_probe,
    .remove = ledclass_plat_remove,
    .driver = {
   
   
        .name = "aml_class_leds",
        .of_match_table = my_of_ids,
        .owner = THIS_MODULE,
    }
};


/*
* 注册 led_platform_driver 结构体到Platform子系统
*/
static int aml_GpioLedClass_plat_init(void)
{
   
   
    int ret_val;
    pr_info("aml_GpioLedClass_plat_init enter\n");

    ret_val = platform_driver_register(&led_platform_driver);
    if (ret_val !=0){
   
   
        pr_err("platform value returned %d\n", ret_val);
        return ret_val;
    }

    pr_info("aml_GpioLedClass_plat_init exit\n");
    return 0;
}

/*
* 从Platform子系统注销 led_platform_driver 结构体
*/
static void aml_GpioLedClass_plat_exit(void)
{
   
   
    pr_info("aml_GpioLedClass_plat_exit enter\n");

    platform_driver_unregister(&led_platform_driver);

    pr_info("aml_GpioLedClass_plat_exit exit\n");
}

module_init(aml_GpioLedClass_plat_init);
module_exit(aml_GpioLedClass_plat_exit);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("szhou <66176468@qq.com>");
MODULE_DESCRIPTION("simple say[5]: led-class device driver");

五、测试

（1）因为LED子系统自动为我们创建了用户接口，所以通过命令行就可以测试对LED的控制。
（2）编译、部署方法，参考之前的系列文章，不再赘述

5.1 加载KO

执行打印：

:/sys/class/leds # insmod /data/aml_gpio_led_class_platform.ko 

[ 2647.823967@3]- aml_GpioLedClass_plat_init enter
[ 2647.824465@3]- ledclass_plat_probe enter
[ 2647.826870@3]- aml_class_leds aml_led_class: gpiod_count = 3 
[ 2647.832558@3]-  ledclass_plat_probe  led(0xe9c8c110)->desc=0xed96b860 
[ 2647.839026@3]- zs, 000000000   
[ 2647.842103@3]- zs, 33333333333333   
[ 2647.846052@3]- zs, platform_probe  devm_led_classdev_register [0], cdev->name=red 
[ 2647.853321@3]-  ledclass_plat_probe  led(0xe9c8c410)->desc=0xed96b820 
[ 2647.859739@3]- zs, 111111111111111   
[ 2647.863350@3]- zs, 33333333333333   
[ 2647.867275@3]- zs, platform_probe  devm_led_classdev_register [1], cdev->name=green 
[ 2647.874691@3]-  ledclass_plat_probe  led(0xe9c8c010)->desc=0xed96b810 
[ 2647.881132@3]- zs, 22222222222   
[ 2647.884409@3]- zs, 33333333333333   
[ 2647.888257@3]- zs, platform_probe  devm_led_classdev_register [2], cdev->name=yellow 
[ 2647.895792@3]- aml_class_leds aml_led_class: ledclass_plat_probe exit
[ 2647.902477@3]- aml_GpioLedClass_plat_init exit
:/sys/class/leds # echo 1 > red/brightness [ 2673.284925@0]-  ENTER led_control  led(0xe9c8c110)->desc=0xed96b860 
[ 2673.285676@0]-  gpiod_set_value(led->desc , 1) 
[ 2673.290656@0]- EXIT led_control

图示如下：
![在这里插入图片描述](https://ucc.alicdn.com/images/user-upload-01/0b508175afbe4d4e88cededed4a28a75.png

5.2 查看设备

如下可见到在probe里面命名的3个LED灯，分别是red、green、yellow

执行打印：

x301:/ # cd /sys/class/leds/
x301:/sys/class/leds # ls -al
total 0
drwxr-xr-x   2 root root 0 2023-01-05 01:16 .
drwxr-xr-x 131 root root 0 2023-01-05 01:16 ..
lrwxrwxrwx   1 root root 0 2023-01-05 01:38 green -> ../../devices/platform/aml_led_class/leds/green
lrwxrwxrwx   1 root root 0 2023-01-05 01:38 pwm_e1 -> ../../devices/platform/pwmleds/leds/pwm_e1
lrwxrwxrwx   1 root root 0 2023-01-05 01:38 red -> ../../devices/platform/aml_led_class/leds/red
lrwxrwxrwx   1 root root 0 2023-01-05 01:38 yellow -> ../../devices/platform/aml_led_class/leds/yellow
x301:/sys/class/leds #

图示如下：

5.3 LED控制

（1）查看LED灯的属性，例如red
x301:/sys/class/leds # cd red/
x301:/sys/class/leds/red # ls -al
total 0
drwxr-xr-x 3 root root    0 2023-01-05 01:33 .
drwxr-xr-x 5 root root    0 2023-01-05 01:33 ..
-rw-r--r-- 1 root root 4096 2023-01-05 01:41 brightness
lrwxrwxrwx 1 root root    0 2023-01-05 01:41 device -> ../../../aml_led_class
-r--r--r-- 1 root root 4096 2023-01-05 01:41 max_brightness
drwxr-xr-x 2 root root    0 2023-01-05 01:41 power
lrwxrwxrwx 1 root root    0 2023-01-05 01:41 subsystem -> ../../../../../class/leds
-rw-r--r-- 1 root root 4096 2023-01-05 01:41 trigger
-rw-r--r-- 1 root root 4096 2023-01-05 01:41 uevent

（2）可见red默认为0，灯灭，符合设定
x301:/sys/class/leds/red # cat brightness
0

（3）点亮红灯
x301:/sys/class/leds/red # echo 1 > brightness
x301:/sys/class/leds/red # cd ..

（4）点亮绿灯
127|x301:/sys/class/leds # echo 1 > green/brightness

（5）点亮黄灯
x301:/sys/class/leds # echo 1 > yellow/brightness
x301:/sys/class/leds #

命令图示如下：

5.4 点灯效果

六、源码下载

• 地址：https://gitee.com/amizhou/amlogic\_t972\_android9\_driver/tree/master/index\_01\_simpleSay\_drivers/lesson\_05

git clone git@gitee.com:amizhou/amlogic_t972_android9_driver.git

七、篇尾

保持持续学习， 欢迎交流。