linux 2.6下编译usb驱动和arm板进行数据通信(4) linux, 通信

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static ssize_t lcd_write(struct file *file, const char __user * user_buffer, size_t count, loff_t *ppos)
{
    struct usb_lcd *dev;
        int retval = 0, r;
    struct urb *urb = NULL;
    char *buf = NULL;
   
    dev = (struct usb_lcd *)file->private_data;
   
    /* verify that we actually have some data to write */
    if (count == 0)
        goto exit;

    r = down_interruptible(&dev->limit_sem);
    if (r < 0)
        return -EINTR;

    /* 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 err_no_buf;
    }
   
    buf = usb_buffer_alloc(dev->udev, count, GFP_KERNEL, &urb->transfer_dma);
    if (!buf) {
        retval = -ENOMEM;
        goto error;
    }
   
    if (copy_from_user(buf, user_buffer, count)) {
        retval = -EFAULT;
        goto error;
    }
   
    /* initialize the urb properly */
    usb_fill_bulk_urb(urb, dev->udev,
              usb_sndbulkpipe(dev->udev, dev->bulk_out_endpointAddr),
              buf, count, lcd_write_bulk_callback, dev);
    urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
   
    /* send the data out the bulk port */
    retval = usb_submit_urb(urb, GFP_KERNEL);
    if (retval) {
        err("USBLCD: %s - failed submitting write urb, error %d", __FUNCTION__, retval);
        goto error;
    }
   
    /* release our reference to this urb, the USB core will eventually free it entirely */
    usb_free_urb(urb);

    r = down_interruptible(&dev->limit_sem);//等待，直到数据完全发送完毕
    up(&dev->limit_sem);
//  mdelay(10);


exit:
    return count;

error:
    usb_buffer_free(dev->udev, count, buf, urb->transfer_dma);
    usb_free_urb(urb);
err_no_buf:
    up(&dev->limit_sem);
    return retval;
}

static const struct file_operations lcd_fops = {
        .owner =        THIS_MODULE,
        .read =         lcd_read,
        .write =        lcd_write,
        .open =         lcd_open,
        .ioctl =        lcd_ioctl,
        .release =      lcd_release,
};