串口驱动分析-打开设备

一、串口驱动程序结构
用户程序通过调用open /dev/... 来实现对串口的打开，其中要通过tty子系统对串口驱动xx_operations的open操作。
samsun.c>>moudle_init(s3c24xx_serial_modinit);>>uart_register_driver(&s3c24xx_uart_drv);

int uart_register_driver(struct uart_driver *drv)
{
    .....

    retval = tty_register_driver(normal);
 out:
    if (retval < 0) {
        put_tty_driver(normal);
        kfree(drv->state);
    }
    return retval;
}

tty_register_driver(normal);

/*
 * Called by a tty driver to register itself.
 */
int tty_register_driver(struct tty_driver *driver)
{
    int error;
    int i;
    dev_t dev;
    void **p = NULL;

    if (!(driver->flags & TTY_DRIVER_DEVPTS_MEM) && driver->num) {
        p = kzalloc(driver->num * 2 * sizeof(void *), GFP_KERNEL);
        if (!p)
            return -ENOMEM;
    }

    if (!driver->major) {
        error = alloc_chrdev_region(&dev, driver->minor_start,
                        driver->num, driver->name);
        if (!error) {
            driver->major = MAJOR(dev);
            driver->minor_start = MINOR(dev);
        }
    } else {
        dev = MKDEV(driver->major, driver->minor_start);
        error = register_chrdev_region(dev, driver->num, driver->name);
    }
    if (error < 0) {
        kfree(p);
        return error;
    }

    if (p) {
        driver->ttys = (struct tty_struct **)p;
        driver->termios = (struct ktermios **)(p + driver->num);
    } else {
        driver->ttys = NULL;
        driver->termios = NULL;
    }

    cdev_init(&driver->cdev, &tty_fops);                                   //这里的注册其实就是注册字符设备
    driver->cdev.owner = driver->owner;
    error = cdev_add(&driver->cdev, dev, driver->num);
    if (error) {
        unregister_chrdev_region(dev, driver->num);
        driver->ttys = NULL;
        driver->termios = NULL;
        kfree(p);
        return error;
    }

    mutex_lock(&tty_mutex);
    list_add(&driver->tty_drivers, &tty_drivers);
    mutex_unlock(&tty_mutex);

    if (!(driver->flags & TTY_DRIVER_DYNAMIC_DEV)) {
        for (i = 0; i < driver->num; i++)
            tty_register_device(driver, i, NULL);
    }
    proc_tty_register_driver(driver);
    driver->flags |= TTY_DRIVER_INSTALLED;
    return 0;
}

第一个入口已找到，tty_fops->tty_open:

static const struct file_operations tty_fops = {
    .llseek        = no_llseek,
    .read        = tty_read,
    .write        = tty_write,
    .poll        = tty_poll,
    .unlocked_ioctl    = tty_ioctl,
    .compat_ioctl    = tty_compat_ioctl,
    .open        = tty_open,
    .release    = tty_release,
    .fasync        = tty_fasync,
};

在tty_open中调用了tty->ops的open:

static int __tty_open(struct inode *inode, struct file *filp)
{
    ......

    if (!retval) {
        if (tty->ops->open)                           //这里调用tty->ops->open
            retval = tty->ops->open(tty, filp);
        else
            retval = -ENODEV;
    }
    filp->f_flags = saved_flags;

    .......
}

tty->ops的tty_operations类型的,uart_ops->uart_open：

static const struct tty_operations uart_ops = {
    .open        = uart_open,
    .close        = uart_close,
    .write        = uart_write,
    .put_char    = uart_put_char,
    .flush_chars    = uart_flush_chars,
    .write_room    = uart_write_room,
    .chars_in_buffer= uart_chars_in_buffer,
    .flush_buffer    = uart_flush_buffer,
    .ioctl        = uart_ioctl,
    .throttle    = uart_throttle,
    .unthrottle    = uart_unthrottle,
    .send_xchar    = uart_send_xchar,
    .set_termios    = uart_set_termios,
    .set_ldisc    = uart_set_ldisc,
    .stop        = uart_stop,
    .start        = uart_start,
    .hangup        = uart_hangup,
    .break_ctl    = uart_break_ctl,
    .wait_until_sent= uart_wait_until_sent,
#ifdef CONFIG_PROC_FS
    .proc_fops    = &uart_proc_fops,
#endif
    .tiocmget    = uart_tiocmget,
    .tiocmset    = uart_tiocmset,
#ifdef CONFIG_CONSOLE_POLL
    .poll_init    = uart_poll_init,
    .poll_get_char    = uart_poll_get_char,
    .poll_put_char    = uart_poll_put_char,
#endif
};

继续看uart_open:

static int uart_open(struct tty_struct *tty, struct file *filp)
{
    .......
    /*
     * Start up the serial port.
     */
    retval = uart_startup(state, 0);      //这里调用了uart_startup;

    ........
}

然后是uart_startup:

static int uart_startup(struct uart_state *state, int init_hw)
{
    struct uart_info *info = &state->info;
    struct uart_port *port = state->port;

    ........

    retval = port->ops->startup(port);       //这里的port是uart_oprt，里面又有一个ops集合，这个集合需要由串口驱动来实现这里是uart_oprt。找到了startup函数

    ........

}

然后继续回到samsung.c中来看uart_ops，通过uart_ops->startup找到了s3c24xx_serial_startup,:

static struct uart_ops s3c24xx_serial_ops = {
    .pm        = s3c24xx_serial_pm,
    .tx_empty    = s3c24xx_serial_tx_empty,
    .get_mctrl    = s3c24xx_serial_get_mctrl,
    .set_mctrl    = s3c24xx_serial_set_mctrl,
    .stop_tx    = s3c24xx_serial_stop_tx,
    .start_tx    = s3c24xx_serial_start_tx,
    .stop_rx    = s3c24xx_serial_stop_rx,
    .enable_ms    = s3c24xx_serial_enable_ms,
    .break_ctl    = s3c24xx_serial_break_ctl,
    .startup    = s3c24xx_serial_startup,
    .shutdown    = s3c24xx_serial_shutdown,
    .set_termios    = s3c24xx_serial_set_termios,
    .type        = s3c24xx_serial_type,
    .release_port    = s3c24xx_serial_release_port,
    .request_port    = s3c24xx_serial_request_port,
    .config_port    = s3c24xx_serial_config_port,
    .verify_port    = s3c24xx_serial_verify_port,
};

static struct s3c24xx_uart_port s3c24xx_serial_ports[CONFIG_SERIAL_SAMSUNG_UARTS] = {              //这里是各个串口
    [0] = {
        .port = {
            .lock        = __SPIN_LOCK_UNLOCKED(s3c24xx_serial_ports[0].port.lock),
            .iotype        = UPIO_MEM,
            .irq        = IRQ_S3CUART_RX0,
            .uartclk    = 0,
            .fifosize    = 16,
            .ops        = &s3c24xx_serial_ops,
            .flags        = UPF_BOOT_AUTOCONF,
            .line        = 0,
        }
    },
    [1] = {
        .port = {
            .lock        = __SPIN_LOCK_UNLOCKED(s3c24xx_serial_ports[1].port.lock),
            .iotype        = UPIO_MEM,
            .irq        = IRQ_S3CUART_RX1,
            .uartclk    = 0,
            .fifosize    = 16,
            .ops        = &s3c24xx_serial_ops,
            .flags        = UPF_BOOT_AUTOCONF,
            .line        = 1,
        }
    },
#if CONFIG_SERIAL_SAMSUNG_UARTS > 2

    [2] = {
        .port = {
            .lock        = __SPIN_LOCK_UNLOCKED(s3c24xx_serial_ports[2].port.lock),
            .iotype        = UPIO_MEM,
            .irq        = IRQ_S3CUART_RX2,
            .uartclk    = 0,
            .fifosize    = 16,
            .ops        = &s3c24xx_serial_ops,
            .flags        = UPF_BOOT_AUTOCONF,
            .line        = 2,
        }
    },
#endif
#if CONFIG_SERIAL_SAMSUNG_UARTS > 3
    [3] = {
        .port = {
            .lock        = __SPIN_LOCK_UNLOCKED(s3c24xx_serial_ports[3].port.lock),
            .iotype        = UPIO_MEM,
            .irq        = IRQ_S3CUART_RX3,
            .uartclk    = 0,
            .fifosize    = 16,
            .ops        = &s3c24xx_serial_ops,
            .flags        = UPF_BOOT_AUTOCONF,
            .line        = 3,
        }
    }
#endif
};

到这里总结一下：tty_operations结构中有open的函数指针，这个对应的open函数是uart_open;这个uart_open调用了uart_ops中的startup函数。
而这个uart_ops是串口对应的函数，从而实现的设备驱动。

二、 串口驱动中的重要数据结构
个人感觉重要的数据结构就是tty_operations和uart_ops，当然和应用层的先是file_operaions。

三、初始化分析

static int s3c24xx_serial_startup(struct uart_port *port)
{
    struct s3c24xx_uart_port *ourport = to_ourport(port);
    int ret;

    dbg("s3c24xx_serial_startup: port=%p (%08lx,%p)\n",
        port->mapbase, port->membase);

    rx_enabled(port) = 1;                                                         //使能串口接收功能

    ret = request_irq(ourport->rx_irq, s3c24xx_serial_rx_chars, 0,
              s3c24xx_serial_portname(port), ourport);                             //注册数据接收中断

    if (ret != 0) {
        printk(KERN_ERR "cannot get irq %d\n", ourport->rx_irq);
        return ret;
    }

    ourport->rx_claimed = 1;

    dbg("requesting tx irq...\n");

    tx_enabled(port) = 1;                                                          //使能发送功能

    ret = request_irq(ourport->tx_irq, s3c24xx_serial_tx_chars, 0,
              s3c24xx_serial_portname(port), ourport);                              //注册数据发送中断

    if (ret) {
        printk(KERN_ERR "cannot get irq %d\n", ourport->tx_irq);
        goto err;
    }

    ourport->tx_claimed = 1;

    dbg("s3c24xx_serial_startup ok\n");

    /* the port reset code should have done the correct
     * register setup for the port controls */
    if (port->line == 2) {
        s3c2410_gpio_cfgpin(S3C2410_GPH6, S3C2410_GPH6_TXD2);
        s3c2410_gpio_pullup(S3C2410_GPH6, 1);
        s3c2410_gpio_cfgpin(S3C2410_GPH7, S3C2410_GPH7_RXD2);
        s3c2410_gpio_pullup(S3C2410_GPH7, 1);
    }

    return ret;

 err:
    s3c24xx_serial_shutdown(port);
    return ret;
}