usb设备驱动入门usb-skeleton之二

进行ch341相关的usb设备读写.
在插入usb设备驱动模块usb-skeleton.ko之后,可通过/dev/skel0文件读写usb设备.　
先写十几个byte的字符, 然后再读设备. 读写/dev/skel0文件的代码如下:

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>


int main(int argc, char* argv[])
{
    int fd; /* File descriptor for the port */
    int i;
    int iRet;
    char *ptr = "1234567890abcdef";
    size_t  count = 16;
    char buf[1024];

    if(argc >= 2) {
        ptr = argv[1];
        count = strlen(argv[1]);
    }
    printf("[%s-%d]tracing: \n", __FILE__, __LINE__);
    fd = open("/dev/skel0", O_RDWR);
    if (fd < 0) { /** error **/
        perror("open");
        printf("[%s-%d] open error!!!\n", __FILE__, __LINE__);
        iRet = fd;
        goto err1;
    }
    //iRet = write(fd, "1234567890abcdef", 16);
    iRet = write(fd, ptr, count);
    if (iRet < 0) {
        printf("[%s-%d] write error!!!\n", __FILE__, __LINE__);
    }

    iRet = read(fd, buf, count);
    if (iRet < 0) {
        printf("[%s-%d] read error!!!\n", __FILE__, __LINE__);
    } else {
        for(i = 0; i < iRet; i++) {
            printf("[0x%02x - %c]", buf[i], buf[i]);
        }
        printf("\n");
    }

    close(fd);
err1:
    return  iRet;
}

１.编译, 运行此代码, 发现ch341接到com串口的一端收到乱码, 并且程序卡住了,　ch341接到com串口的一端发出数据后, 没打印输出, 程序仍卡住. "ctrl+c"也不能退出.
２.从现象可猜测, 数据写的过程已完成, 程序很可能卡在读数据上. 对usb-skeleton.c文件中的skel_read()函数中及其调用的函数中所有可能卡住的地方加"printk("[%s-%d]tracing !\n", __func__, __LINE__);"打印执行路径的语句.　发现代码卡在"wait_for_completion(&dev->bulk_in_completion);"
３.分析其执行条件if (!dev->processed_urb) {...}. 查看代码, 没有发现其它地方对其清零. 也没有初始化清零的动作. 从代码注释看初始化更应该是置1. 猜测是dev->processed_urb初始设置错误. 在skel_probe()函数中加入初始置1的代码"dev->processed_urb = 1;". 重新编译/插入模块/运行代码. 程序运行后停下, ch341接到com串口的一端发出数据后, 有打印输出, 然后程序退出. 至此, 收发操作都有. 然而收到后打印的数据并非ch341对端发出的数据.
４.考虑到ch341芯片是专门用于usb转串口的, 而RS-232串口有特定的通信波特率/校验位/数据位/停止位, 而本实验中并没有进行相应设置. 传输乱码可能的原因是其中一项设置不一致造成的. 抱着试一试的想法, 将ch341接串口一端的串口调试助手的通信波特率由115200到300挨个试, 发现波特率为19200时, ch341接口两端都收到对方发来的数据, 并且数据收发正确. 暂没发现其它问题.

修改后的usb-skeletion.c内容如下:

/*
 * USB Skeleton driver - 2.2
 *
 * Copyright (C) 2001-2004 Greg Kroah-Hartman ([e-mail])
 *
 *    This program is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU General Public License as
 *    published by the Free Software Foundation, version 2.
 *
 * This driver is based on the 2.6.3 version of drivers/usb/usb-skeleton.c
 * but has been rewritten to be easier to read and use.
 *
 */

#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/kref.h>
#include <linux/uaccess.h>
#include <linux/usb.h>
#include <linux/mutex.h>


/* Define these values to match your devices */
#define USB_SKEL_VENDOR_ID    0x1A86
#define USB_SKEL_PRODUCT_ID    0x7523

/* table of devices that work with this driver */
static const struct usb_device_id skel_table[] = {
    { USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) },
    { }                    /* Terminating entry */
};
MODULE_DEVICE_TABLE(usb, skel_table);


/* Get a minor range for your devices from the usb maintainer */
#define USB_SKEL_MINOR_BASE    192

/* our private defines. if this grows any larger, use your own .h file */
#define MAX_TRANSFER        (PAGE_SIZE - 512)
/* MAX_TRANSFER is chosen so that the VM is not stressed by
   allocations > PAGE_SIZE and the number of packets in a page
   is an integer 512 is the largest possible packet on EHCI */
#define WRITES_IN_FLIGHT    8
/* arbitrarily chosen */

/* Structure to hold all of our device specific stuff */
struct usb_skel {
    struct usb_device    *udev;            /* the usb device for this device */
    struct usb_interface    *interface;        /* the interface for this device */
    struct semaphore    limit_sem;        /* limiting the number of writes in progress */
    struct usb_anchor    submitted;        /* in case we need to retract our submissions */
    struct urb        *bulk_in_urb;        /* the urb to read data with */
    unsigned char *bulk_in_buffer;    /* the buffer to receive data */
    size_t            bulk_in_size;        /* the size of the receive buffer */
    size_t            bulk_in_filled;        /* number of bytes in the buffer */
    size_t            bulk_in_copied;        /* already copied to user space */
    __u8            bulk_in_endpointAddr;    /* the address of the bulk in endpoint */
    __u8            bulk_out_endpointAddr;    /* the address of the bulk out endpoint */
    int            errors;            /* the last request tanked */
    int            open_count;        /* count the number of openers */
    bool            ongoing_read;        /* a read is going on */
    bool            processed_urb;        /* indicates we haven't processed the urb */
    spinlock_t        err_lock;        /* lock for errors */
    struct kref        kref;
    struct mutex        io_mutex;        /* synchronize I/O with disconnect */
    struct completion    bulk_in_completion;    /* to wait for an ongoing read */
};
#define to_skel_dev(d) container_of(d, struct usb_skel, kref)

static struct usb_driver skel_driver;
static void skel_draw_down(struct usb_skel *dev);

static void skel_delete(struct kref *kref)
{
    struct usb_skel *dev = to_skel_dev(kref);

    usb_free_urb(dev->bulk_in_urb);
    usb_put_dev(dev->udev);
    kfree(dev->bulk_in_buffer);
    kfree(dev);
}

static int skel_open(struct inode *inode, struct file *file)
{
    struct usb_skel *dev;
    struct usb_interface *interface;
    int subminor;
    int retval = 0;

    subminor = iminor(inode);

    interface = usb_find_interface(&skel_driver, subminor);
    if (!interface) {
        err("%s - error, can't find device for minor %d",
             __func__, subminor);
        retval = -ENODEV;
        goto exit;
    }

    dev = usb_get_intfdata(interface);
    if (!dev) {
        retval = -ENODEV;
        goto exit;
    }

    /* increment our usage count for the device */
    kref_get(&dev->kref);

    /* lock the device to allow correctly handling errors
     * in resumption */
    mutex_lock(&dev->io_mutex);

    if (!dev->open_count++) {
        retval = usb_autopm_get_interface(interface);
            if (retval) {
                dev->open_count--;
                mutex_unlock(&dev->io_mutex);
                kref_put(&dev->kref, skel_delete);
                goto exit;
            }
    } /* else { //uncomment this block if you want exclusive open
        retval = -EBUSY;
        dev->open_count--;
        mutex_unlock(&dev->io_mutex);
        kref_put(&dev->kref, skel_delete);
        goto exit;
    } */
    /* prevent the device from being autosuspended */

    /* save our object in the file's private structure */
    file->private_data = dev;
    mutex_unlock(&dev->io_mutex);

exit:
    return retval;
}

static int skel_release(struct inode *inode, struct file *file)
{
    struct usb_skel *dev;

    dev = file->private_data;
    if (dev == NULL)
        return -ENODEV;

    /* allow the device to be autosuspended */
    mutex_lock(&dev->io_mutex);
    if (!--dev->open_count && dev->interface)
        usb_autopm_put_interface(dev->interface);
    mutex_unlock(&dev->io_mutex);

    /* decrement the count on our device */
    kref_put(&dev->kref, skel_delete);
    return 0;
}

static int skel_flush(struct file *file, fl_owner_t id)
{
    struct usb_skel *dev;
    int res;

    dev = file->private_data;
    if (dev == NULL)
        return -ENODEV;

    /* wait for io to stop */
    mutex_lock(&dev->io_mutex);
    skel_draw_down(dev);

    /* read out errors, leave subsequent opens a clean slate */
    spin_lock_irq(&dev->err_lock);
    res = dev->errors ? (dev->errors == -EPIPE ? -EPIPE : -EIO) : 0;
    dev->errors = 0;
    spin_unlock_irq(&dev->err_lock);

    mutex_unlock(&dev->io_mutex);

    return res;
}

static void skel_read_bulk_callback(struct urb *urb)
{
    struct usb_skel *dev;

    dev = urb->context;

    spin_lock(&dev->err_lock);
    /* sync/async unlink faults aren't errors */
    if (urb->status) {
        if (!(urb->status == -ENOENT ||
            urb->status == -ECONNRESET ||
            urb->status == -ESHUTDOWN))
            err("%s - nonzero write bulk status received: %d",
                __func__, urb->status);

        dev->errors = urb->status;
    } else {
        dev->bulk_in_filled = urb->actual_length;
    }
    dev->ongoing_read = 0;
    spin_unlock(&dev->err_lock);

    complete(&dev->bulk_in_completion);
}

static int skel_do_read_io(struct usb_skel *dev, size_t count)
{
    int rv;

    /* prepare a read */
    usb_fill_bulk_urb(dev->bulk_in_urb,
            dev->udev,
            usb_rcvbulkpipe(dev->udev,
                dev->bulk_in_endpointAddr),
            dev->bulk_in_buffer,
            min(dev->bulk_in_size, count),
            skel_read_bulk_callback,
            dev);
    /* tell everybody to leave the URB alone */
    spin_lock_irq(&dev->err_lock);
    dev->ongoing_read = 1;
    spin_unlock_irq(&dev->err_lock);

    /* do it */
    rv = usb_submit_urb(dev->bulk_in_urb, GFP_KERNEL);
    if (rv < 0) {
        err("%s - failed submitting read urb, error %d",
            __func__, rv);
        dev->bulk_in_filled = 0;
        rv = (rv == -ENOMEM) ? rv : -EIO;
        spin_lock_irq(&dev->err_lock);
        dev->ongoing_read = 0;
        spin_unlock_irq(&dev->err_lock);
    }

    return rv;
}

static ssize_t skel_read(struct file *file, char *buffer, size_t count,
             loff_t *ppos)
{
    struct usb_skel *dev;
    int rv;
    bool ongoing_io;

    dev = file->private_data;

    /* if we cannot read at all, return EOF */
    if (!dev->bulk_in_urb || !count)
        return 0;

    /* no concurrent readers */
    rv = mutex_lock_interruptible(&dev->io_mutex);
    if (rv < 0)
        return rv;

    if (!dev->interface) {        /* disconnect() was called */
        rv = -ENODEV;
        goto exit;
    }

    /* if IO is under way, we must not touch things */
retry:
    spin_lock_irq(&dev->err_lock);
    ongoing_io = dev->ongoing_read;
    spin_unlock_irq(&dev->err_lock);

    if (ongoing_io) {
        /* nonblocking IO shall not wait */
        if (file->f_flags & O_NONBLOCK) {
            rv = -EAGAIN;
            goto exit;
        }
        /*
         * IO may take forever
         * hence wait in an interruptible state
         */
        rv = wait_for_completion_interruptible(&dev->bulk_in_completion);
        if (rv < 0)
            goto exit;
        /*
         * by waiting we also semiprocessed the urb
         * we must finish now
         */
        dev->bulk_in_copied = 0;
        dev->processed_urb = 1;
    }

    if (!dev->processed_urb) {
        /*
         * the URB hasn't been processed
         * do it now
         */
        wait_for_completion(&dev->bulk_in_completion);
        dev->bulk_in_copied = 0;
        dev->processed_urb = 1;
    }

    /* errors must be reported */
    rv = dev->errors;
    if (rv < 0) {
        /* any error is reported once */
        dev->errors = 0;
        /* to preserve notifications about reset */
        rv = (rv == -EPIPE) ? rv : -EIO;
        /* no data to deliver */
        dev->bulk_in_filled = 0;
        /* report it */
        goto exit;
    }

    /*
     * if the buffer is filled we may satisfy the read
     * else we need to start IO
     */

    if (dev->bulk_in_filled) {
        /* we had read data */
        size_t available = dev->bulk_in_filled - dev->bulk_in_copied;
        size_t chunk = min(available, count);

        if (!available) {
            /*
             * all data has been used
             * actual IO needs to be done
             */
            rv = skel_do_read_io(dev, count);
            if (rv < 0)
                goto exit;
            else
                goto retry;
        }
        /*
         * data is available
         * chunk tells us how much shall be copied
         */

        if (copy_to_user(buffer,
                 dev->bulk_in_buffer + dev->bulk_in_copied,
                 chunk))
            rv = -EFAULT;
        else
            rv = chunk;

        dev->bulk_in_copied += chunk;

        /*
         * if we are asked for more than we have,
         * we start IO but don't wait
         */
        if (available < count)
            skel_do_read_io(dev, count - chunk);
    } else {
        /* no data in the buffer */
        rv = skel_do_read_io(dev, count);
        if (rv < 0)
            goto exit;
        else if (!(file->f_flags & O_NONBLOCK))
            goto retry;
        rv = -EAGAIN;
    }
exit:
    mutex_unlock(&dev->io_mutex);
    return rv;
}

static void skel_write_bulk_callback(struct urb *urb)
{
    struct usb_skel *dev;

    dev = urb->context;

    /* sync/async unlink faults aren't errors */
    if (urb->status) {
        if (!(urb->status == -ENOENT ||
            urb->status == -ECONNRESET ||
            urb->status == -ESHUTDOWN))
            err("%s - nonzero write bulk status received: %d",
                __func__, urb->status);

        spin_lock(&dev->err_lock);
        dev->errors = urb->status;
        spin_unlock(&dev->err_lock);
    }

    /* free up our allocated buffer */
    usb_free_coherent(urb->dev, urb->transfer_buffer_length,
              urb->transfer_buffer, urb->transfer_dma);
    up(&dev->limit_sem);
}

static ssize_t skel_write(struct file *file, const char *user_buffer,
              size_t count, loff_t *ppos)
{
    struct usb_skel *dev;
    int retval = 0;
    struct urb *urb = NULL;
    char *buf = NULL;
    size_t writesize = min(count, (size_t)MAX_TRANSFER);

    dev = file->private_data;

    /* verify that we actually have some data to write */
    if (count == 0)
        goto exit;

    /*
     * limit the number of URBs in flight to stop a user from using up all
     * RAM
     */
    if (!(file->f_flags & O_NONBLOCK)) {
        if (down_interruptible(&dev->limit_sem)) {
            retval = -ERESTARTSYS;
            goto exit;
        }
    } else {
        if (down_trylock(&dev->limit_sem)) {
            retval = -EAGAIN;
            goto exit;
        }
    }

    spin_lock_irq(&dev->err_lock);
    retval = dev->errors;
    if (retval < 0) {
        /* any error is reported once */
        dev->errors = 0;
        /* to preserve notifications about reset */
        retval = (retval == -EPIPE) ? retval : -EIO;
    }
    spin_unlock_irq(&dev->err_lock);
    if (retval < 0)
        goto error;

    /* create a urb, and a buffer for it, and copy the data to the urb */
    urb = usb_alloc_urb(0, GFP_KERNEL);
    if (!urb) {
        retval = -ENOMEM;
        goto error;
    }

    buf = usb_alloc_coherent(dev->udev, writesize, GFP_KERNEL,
                 &urb->transfer_dma);
    if (!buf) {
        retval = -ENOMEM;
        goto error;
    }

    if (copy_from_user(buf, user_buffer, writesize)) {
        retval = -EFAULT;
        goto error;
    }

    /* this lock makes sure we don't submit URBs to gone devices */
    mutex_lock(&dev->io_mutex);
    if (!dev->interface) {        /* disconnect() was called */
        mutex_unlock(&dev->io_mutex);
        retval = -ENODEV;
        goto error;
    }

    /* initialize the urb properly */
    usb_fill_bulk_urb(urb, dev->udev,
              usb_sndbulkpipe(dev->udev, dev->bulk_out_endpointAddr),
              buf, writesize, skel_write_bulk_callback, dev);
    urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
    usb_anchor_urb(urb, &dev->submitted);

    /* send the data out the bulk port */
    retval = usb_submit_urb(urb, GFP_KERNEL);
    mutex_unlock(&dev->io_mutex);
    if (retval) {
        err("%s - failed submitting write urb, error %d", __func__,
            retval);
        goto error_unanchor;
    }

    /*
     * release our reference to this urb, the USB core will eventually free
     * it entirely
     */
    usb_free_urb(urb);


    return writesize;

error_unanchor:
    usb_unanchor_urb(urb);
error:
    if (urb) {
        usb_free_coherent(dev->udev, writesize, buf, urb->transfer_dma);
        usb_free_urb(urb);
    }
    up(&dev->limit_sem);

exit:
    return retval;
}

static const struct file_operations skel_fops = {
    .owner =    THIS_MODULE,
    .read =        skel_read,
    .write =    skel_write,
    .open =        skel_open,
    .release =    skel_release,
    .flush =    skel_flush,
    .llseek =    noop_llseek,
};

/*
 * usb class driver info in order to get a minor number from the usb core,
 * and to have the device registered with the driver core
 */
static struct usb_class_driver skel_class = {
    .name =        "skel%d",
    .fops =        &skel_fops,
    .minor_base =    USB_SKEL_MINOR_BASE,
};

static int skel_probe(struct usb_interface *interface,
         const struct usb_device_id *id)
{
    struct usb_skel *dev;
    struct usb_host_interface *iface_desc;
    struct usb_endpoint_descriptor *endpoint;
    size_t buffer_size;
    int i;
    int retval = -ENOMEM;

    /* allocate memory for our device state and initialize it */
    dev = kzalloc(sizeof(*dev), GFP_KERNEL);
    if (!dev) {
        err("Out of memory");
        goto error;
    }
    kref_init(&dev->kref);
    sema_init(&dev->limit_sem, WRITES_IN_FLIGHT);
    mutex_init(&dev->io_mutex);
    spin_lock_init(&dev->err_lock);
    init_usb_anchor(&dev->submitted);
    init_completion(&dev->bulk_in_completion);

    dev->udev = usb_get_dev(interface_to_usbdev(interface));
    dev->interface = interface;

    dev->processed_urb = 1; //!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    /* set up the endpoint information */
    /* use only the first bulk-in and bulk-out endpoints */
    iface_desc = interface->cur_altsetting;
    for (i = 0; i < iface_desc->desc.bNumEndpoints; ++i) {
        endpoint = &iface_desc->endpoint[i].desc;

        if (!dev->bulk_in_endpointAddr &&
            usb_endpoint_is_bulk_in(endpoint)) {
            /* we found a bulk in endpoint */
            buffer_size = le16_to_cpu(endpoint->wMaxPacketSize);
            dev->bulk_in_size = buffer_size;
            dev->bulk_in_endpointAddr = endpoint->bEndpointAddress;
            dev->bulk_in_buffer = kmalloc(buffer_size, GFP_KERNEL);
            if (!dev->bulk_in_buffer) {
                err("Could not allocate bulk_in_buffer");
                goto error;
            }
            dev->bulk_in_urb = usb_alloc_urb(0, GFP_KERNEL);
            if (!dev->bulk_in_urb) {
                err("Could not allocate bulk_in_urb");
                goto error;
            }
        }

        if (!dev->bulk_out_endpointAddr &&
            usb_endpoint_is_bulk_out(endpoint)) {
            /* we found a bulk out endpoint */
            dev->bulk_out_endpointAddr = endpoint->bEndpointAddress;
        }
    }
    if (!(dev->bulk_in_endpointAddr && dev->bulk_out_endpointAddr)) {
        err("Could not find both bulk-in and bulk-out endpoints");
        goto error;
    }

    /* save our data pointer in this interface device */
    usb_set_intfdata(interface, dev);

    /* we can register the device now, as it is ready */
    retval = usb_register_dev(interface, &skel_class);
    if (retval) {
        /* something prevented us from registering this driver */
        err("Not able to get a minor for this device.");
        usb_set_intfdata(interface, NULL);
        goto error;
    }

    /* let the user know what node this device is now attached to */
    dev_info(&interface->dev,
         "USB Skeleton device now attached to USBSkel-%d",
         interface->minor);
    return 0;

error:
    if (dev)
        /* this frees allocated memory */
        kref_put(&dev->kref, skel_delete);
    return retval;
}

static void skel_disconnect(struct usb_interface *interface)
{
    struct usb_skel *dev;
    int minor = interface->minor;

    dev = usb_get_intfdata(interface);
    usb_set_intfdata(interface, NULL);

    /* give back our minor */
    usb_deregister_dev(interface, &skel_class);

    /* prevent more I/O from starting */
    mutex_lock(&dev->io_mutex);
    dev->interface = NULL;
    mutex_unlock(&dev->io_mutex);

    usb_kill_anchored_urbs(&dev->submitted);

    /* decrement our usage count */
    kref_put(&dev->kref, skel_delete);

    dev_info(&interface->dev, "USB Skeleton #%d now disconnected", minor);
}

static void skel_draw_down(struct usb_skel *dev)
{
    int time;

    time = usb_wait_anchor_empty_timeout(&dev->submitted, 1000);
    if (!time)
        usb_kill_anchored_urbs(&dev->submitted);
    usb_kill_urb(dev->bulk_in_urb);
}

static int skel_suspend(struct usb_interface *intf, pm_message_t message)
{
    struct usb_skel *dev = usb_get_intfdata(intf);

    if (!dev)
        return 0;
    skel_draw_down(dev);
    return 0;
}

static int skel_resume(struct usb_interface *intf)
{
    return 0;
}

static int skel_pre_reset(struct usb_interface *intf)
{
    struct usb_skel *dev = usb_get_intfdata(intf);

    mutex_lock(&dev->io_mutex);
    skel_draw_down(dev);

    return 0;
}

static int skel_post_reset(struct usb_interface *intf)
{
    struct usb_skel *dev = usb_get_intfdata(intf);

    /* we are sure no URBs are active - no locking needed */
    dev->errors = -EPIPE;
    mutex_unlock(&dev->io_mutex);

    return 0;
}

static struct usb_driver skel_driver = {
    .name =        "skeleton",
    .probe =    skel_probe,
    .disconnect =    skel_disconnect,
    .suspend =    skel_suspend,
    .resume =    skel_resume,
    .pre_reset =    skel_pre_reset,
    .post_reset =    skel_post_reset,
    .id_table =    skel_table,
    .supports_autosuspend = 1,
};

static int __init usb_skel_init(void)
{
    int result;

    /* register this driver with the USB subsystem */
    result = usb_register(&skel_driver);
    if (result)
        err("usb_register failed. Error number %d", result);

    return result;
}

static void __exit usb_skel_exit(void)
{
    /* deregister this driver with the USB subsystem */
    usb_deregister(&skel_driver);
}

module_init(usb_skel_init);
module_exit(usb_skel_exit);

MODULE_LICENSE("GPL");