平台总线是一种实现设备信息与驱动方法相分离的方法，利用这种方法，我们可以写出一个更像样一点的字符设备驱动，即使用cdev作为接口，平台总线作为分离方式:
xjkeydrv_init()：模块加载函数
└──platform_driver_register()将驱动对象模块注册到平台总线
└──platform_driver.probe()探测函数，提取相应的信息
└──xjkey_init()：初始化cdev对象，创建设备文件等关于cdev接口创建的工作
└──cdev_init():将cdev结构与fops绑定到一起，在fops实现操作接口与控制硬件的逻辑
static struct class *cls =
NULL;
static int major =
0;
static int minor =
0;
const int count =
1;
#define DEVNAME "xjkey"
static struct cdev *xjkeyp =
NULL;
static unsigned long irqflags;
static int irq;
static atomic_t tv;
#if 0
/{
key@
26{
compatible =
"xj4412,key";
interrupt-parent = <&gpx1>;
interrupts = <
2 2>;
};
};
#endif
static irqreturn_t handler_t(int irq, void *dev_id)
{
printk(KERN_INFO
"%s : %s : %d\n", __FILE__, __func__, __LINE__);
return IRQ_HANDLED;
}
//打开设备
static int xjkey_open(struct inode *inode, struct file *filp)
{
//get major and minor from inode
printk(KERN_INFO
"(major=%d, minor=%d), %s : %s : %d\n",
imajor(inode), iminor(inode), __FILE__, __func__, __LINE__);
if(!atomic_dec_and_test(&tv)){
atomic_inc(&tv);
return -EBUSY;
}
return request_irq(irq,
handler_t, irqflags, DEVNAME,
NULL);
}
//关闭设备
static int xjkey_release(struct inode *inode, struct file *filp)
{
//get major and minor from irqflagsinode
printk(KERN_INFO
"(major=%d, minor=%d), %s : %s : %d\n",
imajor(inode), iminor(inode), __FILE__, __func__, __LINE__);
free_irq(irq,
NULL);
atomic_inc(&tv);
return 0;
}
static struct file_operations fops = {
.owner = THIS_MODULE,
.open = xjkey_open,
.release= xjkey_release,
};
static int xjkey_init(void)
{
dev_t devnum;
int ret, i;
struct device *devp =
NULL;
//get command and pid
printk(KERN_INFO
"(%s:pid=%d), %s : %s : %d\n",
current->comm, current->pid, __FILE__, __func__, __LINE__);
//1. alloc cdev objxjkey_init
xjkeyp = cdev_alloc();
if(
NULL == xjkeyp){
return -ENOMEM;
}
//2. init cdev obj
cdev_init(xjkeyp, &fops);
ret = alloc_chrdev_region(&devnum, minor, count, DEVNAME);
if(ret){
goto ERR_STEP;
}
major = MAJOR(devnum);
//3. register cdev obj
ret = cdev_add(xjkeyp, devnum, count);
if(ret){
goto ERR_STEP1;
}
cls = class_create(THIS_MODULE, DEVNAME);
if(IS_ERR(cls)){
ret = PTR_ERR(cls);
goto ERR_STEP1;
}
for(i = minor; i < (count+minor); i++){
devp = device_create(cls,
NULL, MKDEV(major, i),
NULL,
"%s%d", DEVNAME, i);
if(IS_ERR(devp)){
ret = PTR_ERR(devp);
goto ERR_STEP2;
}
}
// init atomic_t
atomic_set(&tv,
1);
//get command and pid
printk(KERN_INFO
"(%s:pid=%d), %s : %s : %d - ok.\n",
current->comm, current->pid, __FILE__, __func__, __LINE__);
return 0;
ERR_STEP2:
for(--i; i >= minor; i--){
device_destroy(cls, MKDEV(major, i));
}
class_destroy(cls);
ERR_STEP1:
unregister_chrdev_region(devnum, count);
ERR_STEP:
cdev_del(xjkeyp);
//get command and pid
printk(KERN_INFO
"(%s:pid=%d), %s : %s : %d - fail.\n",
current->comm, current->pid, __FILE__, __func__, __LINE__);
return ret;
}
static void xjkey_exit(void)
{
int i;
//get command and pid
printk(KERN_INFO
"(%s:pid=%d), %s : %s : %d - leave.\n",
current->comm, current->pid, __FILE__, __func__, __LINE__);
for(i=minor; i < (count+minor); i++){
device_destroy(cls, MKDEV(major, i));
}
class_destroy(cls);
unregister_chrdev_region(MKDEV(major, minor), count);
cdev_del(xjkeyp);
}
static int xjkey_probe(struct platform_device *pdev)
{
struct resource *irq_res;
irq_res = platform_get_resource(pdev, IORESOURCE_IRQ,
0);
if(irq_res){
irq = irq_res->start;
irqflags = irq_res->flags & IRQF_TRIGGER_MASK;
}
else{
printk(KERN_INFO
"No 0 irq\n");
return -EINVAL;
}
return xjkey_init();
}
static int xjkey_remove(struct platform_device *pdev)
{
printk(KERN_INFO
"%s : %s : %d - leave.\n", __FILE__, __func__, __LINE__);
xjkey_exit();
return 0;
}
struct of_device_id of_tbl[] = {
{.compatible =
"xj4412,key",},
{},
};
MODULE_DEVICE_TABLE(of, of_tbl);
//1. alloc obj
static struct platform_driver xjkeydrv = {
.probe = xjkey_probe,
.remove = xjkey_remove,
.driver = {
.name = DEVNAME,
.of_match_table = of_tbl,
},
};
//3. register obj
module_platform_driver(xjkeydrv);
MODULE_LICENSE(
"GPL");
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