如何从内核模块打开/写入/读取uart设备? [英] How do I open/write/read a uart device from a kernel module?

问题描述

该设备是扫描仪.我知道uart5是在dtsi文件中设置的，并且在用户空间中它在/dev/ttymxc4下列出.从用户空间，我了解我可以通过

The device is a scanner. I know uart5 is setup in the dtsi file and in userspace it is listed under /dev/ttymxc4. From userspace, I understand that I can manipulate the device by

fd = open("/dev/ttymxc5", O_RDWR|O_NOCTTY|O_NONBLOCK);
if (fd < 0)
{
    fprintf (stderr,"Open error on %s: %s\n", SCANNER_UART, strerror(errno));
    return nullptr;
}

然后使用termios设置所有设置，例如波特率，使用write调用等写入数据.

And use termios to set all the settings like baudrate, write data using the write call etc.

我想在sysfs下抽象很多命令.我已经像这样设置了"uart驱动程序":

I am wanting to abstract a lot of the commands under sysfs. I've setup a "uart driver" like this:

result = uart_register_driver(&scanner_reg);
if (result)
    return result;

result = uart_add_one_port(&scanner_reg, &scanner_port);
if (result)
    uart_unregister_driver(&scanner_reg);

我正在使用gpio线打开系统和其他一些东西.但是，在原理图中，我看不到这些东西的gpio线.

And I am using gpio lines to turn on the system and a few other things. However, in the schematic, I do not see the gpio lines for these things.

UART5_CTS_HOST_SCAN_3_3V
UART5_RTS_HOST_SCAN_3_3V
UART5_RxD_HOST_SCAN_3_3V
UART5_TxD_HOST_SCAN_3_3V

我只是不确定如何从设备打开/写入/读取数据.我知道关于sys_open和类似的调用，但是我知道它们不是执行此操作的正确"方法；我不想遍历用户空间.

I am just not sure how to open/write/read data from the device. I know about sys_open and similar calls, however, I know they are not the "right" way to do this; I don't want to have to go through userspace.

所以，总而言之，我该怎么办

So, in summary how do I

1. 在模块和"/li"中选择"/dev/ttymxc4设备
2. 打开，设置波特率以及向设备读取/写入数据?

1. "choose" the /dev/ttymxc4 device in my module and
2. open, set baud rate, and read/write data to the device?

谢谢！请帮忙！对于uart来说，它是新事物，我过去曾经处理过i2c，而且似乎不太复杂.

Thanks! Please help! New to everything uart, I've dealt with i2c in the past and it seemed less complicated.

推荐答案

这就是我所做的.我正在从内核而不是使用任何内核本机方法访问uart文件.这是作弊，但有效.所以，

Here's what I did. I am accessing the uart file from the kernel instead of using any kernel native method. This is cheating, but it works. So,

#define SCANNER_UART "/dev/ttymxc4"
...
static int scanner_open(struct inode *inode, struct file *file)
    struct termios term;
...
    scanner_file = filp_open(SCANNER_UART, O_RDWR|O_NOCTTY|O_NONBLOCK, 0);
...
    if (serial_tty_ioctl(scanner_file, TCGETS, (unsigned long)&term) < 0)
    {
        pr_err("%s: Failed to get termios\n", __FUNCTION__);
        return -1;
    }

    term.c_cflag  = B9600 | CLOCAL | CREAD; // 115200 if change, must configure scanner

    /* No parity (8N1) */
    term.c_cflag &= ~PARENB;
    term.c_cflag &= ~CSTOPB;
    term.c_cflag &= ~CSIZE;
    term.c_cflag |= CS8;

    term.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
    term.c_oflag &= ~OPOST;

    term.c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP | INLCR | IGNCR | ICRNL | IXON);

    term.c_cc[VTIME] = 5; // 0.5 seconds read timeout
    term.c_cc[VMIN] = 0;  // read does not block

    if (serial_tty_ioctl(scanner_file, TCSETS, (unsigned long)&term) < 0)
    {
        pr_err("%s: Failed to set termios\n", __FUNCTION__);
        return -1;
    }
...
static const struct file_operations scanner_fops = {
    .owner          = THIS_MODULE,
    .write          = scanner_write,
    .read           = scanner_read,
    .open           = scanner_open,
    .release        = scanner_close,
    .llseek         = no_llseek,
};

struct miscdevice scanner_device = {
    .minor = MISC_DYNAMIC_MINOR,
    .name = "scanner",
    .fops = &scanner_fops,
};

...
    ret = misc_register(&scanner_device);
    if (ret) {
        pr_err("can't misc_register :(\n");
        return ret;
    }

然后，我使用Sysfs向用户提供功能.这是正确的方法吗?可能不是，但这是出于我的目的.它实际上是在将用户空间的实现方式转移到内核.

I then use Sysfs to provide functionality to the user. Is this the right way to do it? Probably not, but it is working for my purposes. It is essentially moving the user-space way of implementing to the kernel.

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