学习笔记 --- MINI2440 linux按键驱动代码分析
知识点：
1 中断初始化流程
2 poll轮询机制
3 misc驱动框架
下面分析MINI2440按键驱动代码：
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define DEVICE_NAME "buttons"
//中断传递的参数
struct button_irq_desc {
int irq;
int pin;
int pin_setting;
int number;
char *name;
};
static struct button_irq_desc button_irqs [] = {
{IRQ_EINT8 , S3C2410_GPG(0) , S3C2410_GPG0_EINT8 , 0, "KEY0"},
{IRQ_EINT11, S3C2410_GPG(3) , S3C2410_GPG3_EINT11 , 1, "KEY1"},
{IRQ_EINT13, S3C2410_GPG(5) , S3C2410_GPG5_EINT13 , 2, "KEY2"},
{IRQ_EINT14, S3C2410_GPG(6) , S3C2410_GPG6_EINT14 , 3, "KEY3"},
{IRQ_EINT15, S3C2410_GPG(7) , S3C2410_GPG7_EINT15 , 4, "KEY4"},
{IRQ_EINT19, S3C2410_GPG(11), S3C2410_GPG11_EINT19, 5, "KEY5"},
};
static volatile char key_values [] = {'0', '0', '0', '0', '0', '0'};
//定义一个等待队列,相当于ucos的定义一个队列变量
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);
//等待队列触发的条件变量，如果为1唤醒等待进程,为0继续休眠
static volatile int ev_press = 0;
//dev_id可以传入全局的表达这个驱动的结构体
//dev_id传入中断可以直接访问这些数据
static irqreturn_t buttons_interrupt(int irq, void *dev_id)
{
struct button_irq_desc *button_irqs = (struct button_irq_desc *)dev_id;
int down;
down = !s3c2410_gpio_getpin(button_irqs->pin); //中断发生读取按键的状态
if (down != (key_values[button_irqs->number] & 1)) { //检查按键值是否一致(防抖)
key_values[button_irqs->number] = '0' + down; //赋按键值
ev_press = 1; //先使能条件，表示唤醒条件OK
wake_up_interruptible(&button_waitq); //再通知button_waitq 去触发唤醒
}
return IRQ_RETVAL(IRQ_HANDLED);
}
static int s3c24xx_buttons_open(struct inode *inode, struct file *file)
{
int i;
int err = 0;
for (i = 0; i < sizeof(button_irqs)/sizeof(button_irqs[0]); i++) {
if (button_irqs[i].irq < 0) {
continue;
}
err = request_irq(button_irqs[i].irq, buttons_interrupt, IRQ_TYPE_EDGE_BOTH,
button_irqs[i].name, (void *)&button_irqs[i]);
//打开的时候注册中断，内部会通过IRQ_TYPE_EDGE_BOTH来自动配置引脚
if (err)
break;
}
if (err) {
i--;
for (; i >= 0; i--) {
if (button_irqs[i].irq < 0) {
continue;
}
disable_irq(button_irqs[i].irq); //如果有一个注册失败，则取消前面已经注册了的
free_irq(button_irqs[i].irq, (void *)&button_irqs[i]);
}
return -EBUSY;
}
ev_press = 1;
return 0;
}
static int s3c24xx_buttons_close(struct inode *inode, struct file *file)
{
int i;
for (i = 0; i < sizeof(button_irqs)/sizeof(button_irqs[0]); i++) {
if (button_irqs[i].irq < 0) {
continue;
}
free_irq(button_irqs[i].irq, (void *)&button_irqs[i]); //关闭的时候要释放中断
}
return 0;
}
static int s3c24xx_buttons_read(struct file *filp, char __user *buff, size_t count, loff_t *offp)
{
unsigned long err;
if (!ev_press) {
if (filp->f_flags & O_NONBLOCK) //如果不阻塞,则直接返回
return -EAGAIN;
else
wait_event_interruptible(button_waitq, ev_press);
//一直在休眠等待ev_press条件置位之后就唤醒,这个条件在中断里面触发
}
ev_press = 0;
err = copy_to_user(buff, (const void *)key_values, min(sizeof(key_values), count));
return err ? -EFAULT : min(sizeof(key_values), count);
}
/*
poll机制:
这个是提供给应用的另一种获取按键信息的方式
相当于ucos的超时等待一个信号量,如果事件到了就唤醒，否则一直休眠
如果不使用poll，只使用wait_event_interruptible(button_waitq, ev_press); 方式一直傻等
那么应用程序read的时候会一直堵塞,相当于ucos里面的事件超时设置为0
有了poll机制就可以使用超时等待
查看内核源码:
app:poll
kernel: sys_poll(struct pollfd __user *ufds, unsigned int nfds, long timeout_msecs)
timeout_jiffies = msecs_to_jiffies(timeout_msecs); //配置超时时间
do_sys_poll(ufds, nfds, &timeout_jiffies);
poll_initwait(&table); //初始化等待队列
init_poll_funcptr(&pwq->pt, __pollwait);
pt->qproc = qproc; //table->pt->qproc= __pollwait;
do_poll(nfds, head, &table, timeout);
for (;;)
{
for (; pfd != pfd_end; pfd++) //针对多个进程
{
if (do_pollfd(pfd, pt)) //内部:mask = file->f_op->poll(file, pwait); f_op->poll就是写得驱动
{
count++; pt = NULL;
}
}
// 若count不为0或者超时或者有事件发生则会跳出死循环
if (count || !*timeout || signal_pending(current))
break;
//若count为0且未超时且无事件发生则会休眠__timeout时间
schedule_timeout(__timeout);
}
*/
static unsigned int s3c24xx_buttons_poll( struct file *file, struct poll_table_struct *wait)
{
unsigned int mask = 0;
//把当前进程挂载到等待队列中，此时还没有休眠
poll_wait(file, &button_waitq, wait);
if (ev_press)
mask |= POLLIN | POLLRDNORM;
return mask; //这里返回0之后进程就休眠了,如果不为0，代表进程唤醒
}
static struct file_operations dev_fops = {
.owner = THIS_MODULE,
.open = s3c24xx_buttons_open,
.release = s3c24xx_buttons_close,
.read = s3c24xx_buttons_read,
.poll = s3c24xx_buttons_poll,
};
static struct miscdevice misc = {
.minor = MISC_DYNAMIC_MINOR,
.name = DEVICE_NAME,
.fops = &dev_fops,
};
static int __init dev_init(void)
{
int ret;
/*这个驱动注册为misc类型的驱动
misc本身是一个字符驱动，它可以很方便的注册驱动
相当于一个框架已经搭好了的字符设备驱动
最大的作用就是驱动注册后自动通过udev 的class机制去创建设备节点
*/
ret = misc_register(&misc);
printk (DEVICE_NAME"\tinitialized\n");
return ret;
}
static void __exit dev_exit(void)
{
misc_deregister(&misc);
}
module_init(dev_init);
module_exit(dev_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("FriendlyARM Inc.");
测试程序：
int main(int argc, char **argv)
{
int fd;
unsigned char key_val;
int ret;
struct pollfd fds[1]; //poll可以轮询多个文件(设备)，这里只设置轮询一个
fd = open("/dev/buttons", O_RDWR);
if (fd < 0)
{
printf("can't open!\n");
}
fds[0].fd = fd; //设置轮询的文件
fds[0].events = POLLIN; //设置触发的事件,这个值和poll驱动返回的值做比较，有这个事件则唤醒
while (1)
{
ret = poll(fds, 1, 5000); //使用了轮询机制，轮询一个文件， 5s未触发则超时返回0
if (ret == 0)
{
printf("time out\n");
}
else
{
read(fd, &key_val, 1); //如果这个循环里面如果只用这行来等待，就会一直休眠了，无超时的概念；这里使用了poll机制，让poll去检测触发事件
printf("key_val = 0x%x\n", key_val);
}
}
return 0;
}上面写得驱动我们看到没有看到初始化中断的GPIO口和初始化中断的代码，打开设备就只注册中断，其实在注册中断的时候会调用struct irq_chip里面的set_type去初始化：
request_irq会执行到这个来配置中断：
ret = __irq_set_trigger(desc, irq, new->flags & IRQF_TRIGGER_MASK);而这个函数执行的就是在系统初始化中断时设置好的set_type，看下：
最开始：
MACHINE_START(MINI2440, "FriendlyARM Mini2440 development board")
.phys_io = S3C2410_PA_UART,
.io_pg_offst = (((u32)S3C24XX_VA_UART) >> 18) & 0xfffc,
.boot_params = S3C2410_SDRAM_PA + 0x100,
.init_irq = s3c24xx_init_irq,
.map_io = mini2440_map_io,
.init_machine = mini2440_machine_init,
.timer = &s3c24xx_timer,
MACHINE_ENDs3c24xx_init_irq初始化中断的时候会设置好中断：
void __init s3c24xx_init_irq(void)
{
unsigned long pend;
unsigned long last;
int irqno;
int i;
#ifdef CONFIG_FIQ
init_FIQ();
#endif
irqdbf("s3c2410_init_irq: clearing interrupt status flags\n");
/* first, clear all interrupts pending... */
last = 0;
for (i = 0; i < 4; i++) {
pend = __raw_readl(S3C24XX_EINTPEND);
if (pend == 0 || pend == last)
break;
__raw_writel(pend, S3C24XX_EINTPEND);
printk("irq: clearing pending ext status %08x\n", (int)pend);
last = pend;
}
last = 0;
for (i = 0; i < 4; i++) {
pend = __raw_readl(S3C2410_INTPND);
if (pend == 0 || pend == last)
break;
__raw_writel(pend, S3C2410_SRCPND);
__raw_writel(pend, S3C2410_INTPND);
printk("irq: clearing pending status %08x\n", (int)pend);
last = pend;
}
last = 0;
for (i = 0; i < 4; i++) {
pend = __raw_readl(S3C2410_SUBSRCPND);
if (pend == 0 || pend == last)
break;
printk("irq: clearing subpending status %08x\n", (int)pend);
__raw_writel(pend, S3C2410_SUBSRCPND);
last = pend;
}
/* register the main interrupts */
irqdbf("s3c2410_init_irq: registering s3c2410 interrupt handlers\n");
for (irqno = IRQ_EINT4t7; irqno <= IRQ_ADCPARENT; irqno++) {
/* set all the s3c2410 internal irqs */
switch (irqno) {
/* deal with the special IRQs (cascaded) */
case IRQ_EINT4t7:
case IRQ_EINT8t23:
case IRQ_UART0:
case IRQ_UART1:
case IRQ_UART2:
case IRQ_ADCPARENT:
set_irq_chip(irqno, &s3c_irq_level_chip);
set_irq_handler(irqno, handle_level_irq);
break;
case IRQ_RESERVED6:
case IRQ_RESERVED24:
/* no IRQ here */
break;
default:
//irqdbf("registering irq %d (s3c irq)\n", irqno);
set_irq_chip(irqno, &s3c_irq_chip);
set_irq_handler(irqno, handle_edge_irq);
set_irq_flags(irqno, IRQF_VALID);
}
}
/* setup the cascade irq handlers */
set_irq_chained_handler(IRQ_EINT4t7, s3c_irq_demux_extint4t7);
set_irq_chained_handler(IRQ_EINT8t23, s3c_irq_demux_extint8);
set_irq_chained_handler(IRQ_UART0, s3c_irq_demux_uart0);
set_irq_chained_handler(IRQ_UART1, s3c_irq_demux_uart1);
set_irq_chained_handler(IRQ_UART2, s3c_irq_demux_uart2);
set_irq_chained_handler(IRQ_ADCPARENT, s3c_irq_demux_adc);
/* external interrupts */
for (irqno = IRQ_EINT0; irqno <= IRQ_EINT3; irqno++) {
irqdbf("registering irq %d (ext int)\n", irqno);
set_irq_chip(irqno, &s3c_irq_eint0t4);
set_irq_handler(irqno, handle_edge_irq);
set_irq_flags(irqno, IRQF_VALID);
}
for (irqno = IRQ_EINT4; irqno <= IRQ_EINT23; irqno++) {
irqdbf("registering irq %d (extended s3c irq)\n", irqno);
set_irq_chip(irqno, &s3c_irqext_chip);
set_irq_handler(irqno, handle_edge_irq);
set_irq_flags(irqno, IRQF_VALID);
}
/* register the uart interrupts */
irqdbf("s3c2410: registering external interrupts\n");
for (irqno = IRQ_S3CUART_RX0; irqno <= IRQ_S3CUART_ERR0; irqno++) {
irqdbf("registering irq %d (s3c uart0 irq)\n", irqno);
set_irq_chip(irqno, &s3c_irq_uart0);
set_irq_handler(irqno, handle_level_irq);
set_irq_flags(irqno, IRQF_VALID);
}
for (irqno = IRQ_S3CUART_RX1; irqno <= IRQ_S3CUART_ERR1; irqno++) {
irqdbf("registering irq %d (s3c uart1 irq)\n", irqno);
set_irq_chip(irqno, &s3c_irq_uart1);
set_irq_handler(irqno, handle_level_irq);
set_irq_flags(irqno, IRQF_VALID);
}
for (irqno = IRQ_S3CUART_RX2; irqno <= IRQ_S3CUART_ERR2; irqno++) {
irqdbf("registering irq %d (s3c uart2 irq)\n", irqno);
set_irq_chip(irqno, &s3c_irq_uart2);
set_irq_handler(irqno, handle_level_irq);
set_irq_flags(irqno, IRQF_VALID);
}
for (irqno = IRQ_TC; irqno <= IRQ_ADC; irqno++) {
irqdbf("registering irq %d (s3c adc irq)\n", irqno);
set_irq_chip(irqno, &s3c_irq_adc);
set_irq_handler(irqno, handle_edge_irq);
set_irq_flags(irqno, IRQF_VALID);
}
irqdbf("s3c2410: registered interrupt handlers\n");
}
for (irqno = IRQ_EINT4; irqno <= IRQ_EINT23; irqno++) {
irqdbf("registering irq %d (extended s3c irq)\n", irqno);
set_irq_chip(irqno, &s3c_irqext_chip);
set_irq_handler(irqno, handle_edge_irq);
set_irq_flags(irqno, IRQF_VALID);
}
chip设置为：
static struct irq_chip s3c_irqext_chip = {
.name = "s3c-ext",
.mask = s3c_irqext_mask,
.unmask = s3c_irqext_unmask,
.ack = s3c_irqext_ack,
.set_type = s3c_irqext_type,
.set_wake = s3c_irqext_wake
};mask unmask：中断屏蔽/打开
ack：清中断标志位
set_type：将管脚设置为中断功能，设置中断触发类型
内核已经搭建好了一个中断框架，我们只需要去按照要求填写这个结构体就可以了，真正需要的中断处理在request_irq的时候传入中断服务函数；