Android字符设备驱动开发基于高通msm8916【原创 】

本人才疏浅学，写一篇文档总结自己在msm8916平台上移植自己编写的简单的字符设备驱动开发的整个流程。这个小项目的主要功能是开发一个简单的APP，APP通过JNI去调用位于kernel的字符设备驱动。

APP的设计，开发平台Android Studio

主要的文件是下面的三个文件：

MainActivity.java文件的内容如下：

 package com.example.administrator.myled;

 import android.nfc.Tag;
 import android.support.v7.app.AppCompatActivity;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.View;
 import android.widget.Button;
 import android.widget.Toast;

 import com.zbahuang.led.lowlevel.LedNative;

 public class MainActivity extends AppCompatActivity implements View.OnClickListener {
     private final static String TAG = "zbzhuang";
     Button btn_led_on;
     Button btn_led_off;
     LedNative myled;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);

         initUI();

         myled = new LedNative();
         myled.openDev();
         Log.d(TAG,"app:open Dev");
     }

     private void initUI() {
         btn_led_on = (Button) findViewById(R.id.btn_led_on);
         btn_led_on.setOnClickListener(this);

         btn_led_off = (Button) findViewById(R.id.btn_led_off);
         btn_led_off.setOnClickListener(this);
     }

     @Override
     public void onClick(View v) {
         switch (v.getId()){
             case R.id.btn_led_on:
                 Toast.makeText(MainActivity.this,"拉灯-->",Toast.LENGTH_SHORT).show();
                 Log.d(TAG,"app:LED on");
                 myled.devOn();
                 break;
             case R.id.btn_led_off:
                 Toast.makeText(MainActivity.this,"灭灯-->",Toast.LENGTH_SHORT).show();
                 Log.d(TAG,"app:LED off");
                 myled.devOff();
                 break;
             default:
                 break;
         }

     }

     @Override
     protected void onDestroy() {
         super.onDestroy();
         myled.closeDev();
         Log.d(TAG,"app:close Dev");
     }
 }

LedNative.java文件的内容如下：
在这个文件中所声明的方法是在jni中实现的啊。使用了特殊的关键字表示该方法是在JNI当中实现的啊。

 package com.zbahuang.led.lowlevel;

 /**
  * Created by Administrator on 2017/3/29 0029.
  */

 public class LedNative {

     static {
         System.loadLibrary("led_jni");
     }

     public native int openDev();
     public native int devOn();
     public native int devOff();
     public native int closeDev();
 }
 package com.zbahuang.led.lowlevel;

 /**
  * Created by Administrator on 2017/3/29 0029.
  */

 public class LedNative {

     static {
         System.loadLibrary("led_jni");
     }

     public native int openDev();
     public native int devOn();
     public native int devOff();
     public native int closeDev();
 }

activity_main.xml文件的内容如下：

 <?xml version="1.0" encoding="utf-8"?>
 <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     tools:context="com.example.administrator.myled.MainActivity">

     <RelativeLayout
         android:layout_width="394dp"
         android:layout_height="520dp"
         tools:layout_editor_absoluteX="-5dp"
         tools:layout_editor_absoluteY="-10dp">

         <Button
             android:id="@+id/btn_led_on"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_alignParentStart="true"
             android:layout_alignParentTop="true"
             android:layout_marginStart="56dp"
             android:layout_marginTop="109dp"
             android:text="拉灯" />

         <Button
             android:id="@+id/btn_led_off"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_alignBaseline="@+id/btn_led_on"
             android:layout_alignBottom="@+id/btn_led_on"
             android:layout_marginStart="81dp"
             android:layout_toEndOf="@+id/btn_led_on"
             android:text="灭灯" />
     </RelativeLayout>
 </android.support.constraint.ConstraintLayout>

JNI的文件：

led_jni.cpp

 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <errno.h>
 #include <string.h>

 #define LOG_TAG "zbzhuang"
 #include <utils/Log.h>

 #include "jni.h"

 static jint fd;

 static jint open_led(JNIEnv *env,jobject thiz)
 {
     ALOGD("JNI:-----------%s--------------",__FUNCTION__);

     fd = open("/dev/led1",O_RDWR);
     if(fd < ){
         ALOGD("JNI:open error:%s\n",strerror(errno));
         return -;
     }

     return ;
 }

 static jint led_on(JNIEnv *env,jobject thiz)
 {
     ALOGD("JNI:-----------%s--------------",__FUNCTION__);
     jint ret ;
     jint on = ;

     ret = write(fd,&on,);
     if(ret < ){
         ALOGD("JNI:write off error:%s\n",strerror(errno));
         return -;
     }

     return ;
 }

 static jint led_off(JNIEnv *env,jobject thiz)
 {
     ALOGD("JNI:-----------%s--------------",__FUNCTION__);
     jint ret;
     jint off = ;

     ret = write(fd,&off,);
     if(ret < ){
         ALOGD("JNI:write off error:%s\n",strerror(errno));
         return -;
     }

     return ;
 }

 static jint close_led(JNIEnv *env,jobject thiz)
 {
     ALOGD("JNI:-----------%s--------------",__FUNCTION__);
     close(fd);

     return ;
 }

 const JNINativeMethod  led_jni_methods[] = {
     {"openDev","()I",(void *)open_led},
     {"devOn","()I",(void *)led_on},
     {"devOff","()I",(void *)led_off},
     {"closeDev","()I",(void *)close_led},

 };

 jint JNI_OnLoad(JavaVM * vm,void * reserved)
 {
     JNIEnv *env = NULL;
     jint ret ;

     ALOGD("%s[%s:%d]JNI:--------------^_&--------------------\n",__func__,__FILE__,__LINE__);
     ret = vm->GetEnv((void * *)&env,JNI_VERSION_1_4);
     if(ret != JNI_OK){
         ALOGE("JNI:vm->GetEnv error");
         return -;
     }

     jclass clz = env->FindClass("com/zbahuang/led/lowlevel/LedNative");

     if(clz == NULL){
         ALOGE("%s[%s:%d]JNI:env->FindClass error",__func__,__FILE__,__LINE__);
         return -;
     }

     ret = env->RegisterNatives(clz,
                 led_jni_methods,
                 sizeof(led_jni_methods)/sizeof(led_jni_methods[]));

     if(ret < ){
         ALOGE("%s[%s:%d]JNI:env->RegisterNatives error\n",__func__,__FILE__,__LINE__);
         return -;
     }

     return JNI_VERSION_1_4;

 }

Android.mk

 LOCAL_PATH:= $(call my-dir)
 include $(CLEAR_VARS)

 LOCAL_MODULE_TAGS := optional

 LOCAL_MODULE:= libled_jni

 LOCAL_SRC_FILES:= \
   led_jni.cpp

 LOCAL_SHARED_LIBRARIES := \
     libutils liblog

 LOCAL_C_INCLUDES += \
     $(JNI_H_INCLUDE)

 include $(BUILD_SHARED_LIBRARY)

执行：       mmm mytest/led_jni/   之后会生成动态库放在  out/target/product/msm8916_64/obj/lib/libled_jni.so

将这个库推送到平板电脑就可以通过这个库去调用驱动。

内核的驱动文件：kernel/drivers/input/misc/led.c

 /*1. 头文件*/
 #include<linux/init.h>
 #include<linux/module.h>
 #include<linux/fs.h>
 #include<linux/device.h>
 #include<linux/slab.h>
 #include<linux/cdev.h>
 #include<asm/uaccess.h>
 #include<asm/io.h>

 static unsigned int led_major=;
 volatile unsigned long *gpc0con = NULL;
 volatile unsigned long *gpc0dat = NULL;

 struct led_device{
     struct class *led_class ;    //表示一类设备, 存储某些信息
     struct device *led_device ;    //表示一个设备
     struct cdev  *led_cdev;
     unsigned int val;

 };

 struct led_device *s5pv_led_dev;

 /*可用于查询LED的状态*/
 static ssize_t led_read(struct file *file, char __user *buf, size_t count, loff_t *opps)
 {
     int ret;

     ret = copy_to_user(buf, &s5pv_led_dev->val, count);
     if(ret>)
     {
         printk(KERN_ERR "zbzhuang### copy to user failed!\n");
         return ret;
     }

     printk(KERN_INFO "zbzhuang### val=%d\n", s5pv_led_dev->val);

     return ret?:count;
 }
 static ssize_t led_write(struct file *file, const char __user *buf, size_t count, loff_t *opps)
 {
     int ret;

     /*拷贝成功,返回0; 拷贝失败, 返回没有被拷贝的字节数*/
     ret = copy_from_user(&s5pv_led_dev->val, buf, count);
     if(ret>)
     {
         printk(KERN_ERR "zbzhuang### copy from user failed!\n");
         return ret;
     }

     if(s5pv_led_dev->val)
     {
         /*点亮LED*/
         //*gpc0dat |= ((0x1<<3)|(0x1<<4));
         printk(KERN_ERR "zbzhuang### led on\n");
     }
     else
     {
         /*熄灭LED*/
 //        *gpc0dat &= ~((0x1<<3)|(0x1<<4));
         printk(KERN_ERR "zbzhuang### led off\n");
     }

     return ret?:count;
 }

 static int led_open(struct inode *inode, struct file *file)
 {
 #if 0
     /*1. 将物理地址映射为虚拟地址*/
     gpc0con = ioremap(0xE0200060, );
     gpc0dat = gpc0con +;

     /*2. 初始化GPC0_3,4引脚功能为输出*/
     *gpc0con &= ~((0xf<<)|(0xf<<));
     *gpc0con |=  ((0x1<<)|(0x1<<));
 #endif
     printk(KERN_ERR "zbzhuang### -----------%s-------------\n",__FUNCTION__);

     return ;
 }

 static int led_close(struct inode *inode, struct file *file)
 {
 #if 0

     *gpc0con &= ~((0xf<<)|(0xf<<));
     iounmap(gpc0con);
 #endif
     printk(KERN_ERR "zbzhuang### ------------%s-----------------\n",__FUNCTION__);

     return ;

 }

 /*硬件操作方法*/
 struct file_operations led_fops={
     .owner = THIS_MODULE,    //当前模块所用
     .open  = led_open,
     .write = led_write,
     .read  = led_read,
     .release = led_close,

 };

 static void setup_led_cdev(void)
 {
     /*1. 为cdev结构体分配空间*/
     s5pv_led_dev->led_cdev = cdev_alloc();

     /*2. 初始化cdev结构体*/
     cdev_init(s5pv_led_dev->led_cdev, &led_fops);

     /*3. 注册cdev,加载到内核哈希表中*/
     cdev_add(s5pv_led_dev->led_cdev, MKDEV(led_major, ), );

 }

 /*2. 实现模块加载函数*/
 static int __init led_init(void)
 {
     dev_t devno;
     int ret;
     /*1. 新的申请主设备号的方法*/
     if(led_major)
     {
         /*静态申请*/
         devno = MKDEV(led_major, );
         register_chrdev_region(devno, , "led");
     }
     else
     {
         /*动态申请*/
         alloc_chrdev_region(&devno, , , "led");
         led_major = MAJOR(devno);
     }

     /*2. 为本地结构体分配空间*/

         /*
         **    param1: 大小
         **    param2:    标号: GFP_KERNEL--->表示如果分配不成功,则休眠
         */
     s5pv_led_dev = kmalloc(sizeof(struct led_device), GFP_KERNEL);
     if (!s5pv_led_dev)
     {
         printk(KERN_ERR "zbzhuang NO memory for malloc!\n");
         ret = -ENOMEM;
         goto out_err_1;
     }

     /*3. 构建struct cdev结构体*/
     setup_led_cdev();

     /*4. 创建设备文件*/
     /*
     **    param1:    struct class
     **    param2:    父类, 一般为NULL
     **    param3:    dev_t ---> 表示一个设备号, 是一个无符号32位整形
     **                        其中高12位为主设备号, 低20为次设备号
     **            如何操作设备号: MKDEV(major, minor)根据主设备号和次设备号组成一个设备号
     */    

     s5pv_led_dev->led_class = class_create(THIS_MODULE, "led_class");
     if (IS_ERR(s5pv_led_dev->led_class)) {
         printk(KERN_ERR "zbzhuang class_create() failed for led_class\n");
         ret = -EINVAL;
         goto out_err_2;
     }

     s5pv_led_dev->led_device = device_create(s5pv_led_dev->led_class, NULL, MKDEV(led_major, ), NULL, "led1");    // 创建设备文件/dev/led1
     if (IS_ERR(s5pv_led_dev->led_device)) {
         printk(KERN_ERR "zbzhuang device_create failed for led_device\n");
         ret = -ENODEV;
         goto out_err_3;
     }

     return ;

 out_err_3:
     class_destroy(s5pv_led_dev->led_class);

 out_err_2:
     cdev_del(s5pv_led_dev->led_cdev);
     kfree(s5pv_led_dev);

 out_err_1:
     unregister_chrdev_region(MKDEV(led_major, ), );
     return ret;

 }

 /*3. 实现模块卸载函数*/
 static void __exit led_exit(void)
 {
     unregister_chrdev_region(MKDEV(led_major, ), );
     device_destroy(s5pv_led_dev->led_class, MKDEV(led_major, ));
     class_destroy(s5pv_led_dev->led_class);
     cdev_del(s5pv_led_dev->led_cdev);
     kfree(s5pv_led_dev);
 }

 /*4. 模块许可声明*/
 module_init(led_init);
 module_exit(led_exit);
 MODULE_LICENSE("GPL");

修改kconfig和makefile，在内核当中添加：

makefile

kconfig:

修改这个文件将驱动编译进内核:kernel/arch/arm64/configs/msm_defconfig  与msm-perf_deconfig

之后使用adb工具将重新编译的boot.imge镜像重新烧录就可以了啊。

看看log的输出验证一下结果：

android studio查看log的结果：

adb查看log的结果：

从app到jni到kernel，整个调用的过程成功。

如果出现打开设备失败的话在system/core/rootdir/uevent.rc中添加设备节点的权限777即可。