Usb设备驱动4：usb-skeleton例程
有了前面的设备驱动基础，以及usb方面的基础知识，则可以很轻松的就理解usb-skeleton例程，并轻松的就能写出自己的简易usb driver了。
下面是usb-skeleton例程的简易解析：
/*
* USB Skeleton driver - 2.0
*
* Copyright (C) 2001-2004 Greg Kroah-Hartman (greg@kroah.com)
*
* 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 easy to read and use, as no locks are now
* needed anymore.
*
*/
#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 <asm/uaccess.h>
#include <linux/usb.h>
/* Define these values to match your devices */
#define USB_SKEL_VENDOR_ID 0xfff0
#define USB_SKEL_PRODUCT_ID 0xfff0
/* table of devices that work with this driver */
static 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 )
#define WRITES_IN_FLIGHT 8
/* 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 */
unsigned char * bulk_in_buffer; /* the buffer to receive data */
size_t bulk_in_size; /* the size of the receive buffer */
__u8 bulk_in_endpointAddr; /* the address of the bulk in endpoint */
__u8 bulk_out_endpointAddr; /* the address of the bulk out endpoint */
struct kref kref;
};
#define to_skel_dev(d) container_of(d, struct usb_skel, kref)
static struct usb_driver skel_driver;
static void skel_delete(struct kref *kref)
{
/*
1.获得设备
2.减少设备的引用次数
3.释放分配的数据空间
4.释放分配的驱动空间
*/
struct usb_skel *dev = to_skel_dev(kref);
usb_put_dev(dev->udev);
kfree (dev->bulk_in_buffer);
kfree (dev);
}
static int skel_open(struct inode *inode, struct file *file)
{
/*
1.通过驱动结构体和此设备号，获得设备接口
2.通过接口，获得设备结构体
3.增加设备的引用次数
4.把设备驱动跟文件句柄关联起来，便于后面使用
5.
6.
*/
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",
__FUNCTION__, 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);
/* save our object in the file's private structure */
file->private_data = dev;
exit:
return retval;
}
static int skel_release(struct inode *inode, struct file *file)
{
/*
减少设备的引用次数
*/
struct usb_skel *dev;
dev = (struct usb_skel *)file->private_data;
if (dev == NULL)
return -ENODEV;
/* decrement the count on our device */
kref_put(&dev->kref, skel_delete);
return 0;
}
static ssize_t skel_read(struct file *file, char *buffer, size_t count, loff_t *ppos)
{
/*
读数据函数的功能，主要实现如下:
1.通过文件句柄，获得设备驱动数据
2.通过设备驱动数据的操作集，向设备发送获得数据的命令
3.获得从设备返回的数据
4.把数据从内核空间复制到用户空间
5.
*/
struct usb_skel *dev;
int retval = 0;
int bytes_read;
dev = (struct usb_skel *)file->private_data;
/* do a blocking bulk read to get data from the device */
retval = usb_bulk_msg(dev->udev,
usb_rcvbulkpipe(dev->udev, dev->bulk_in_endpointAddr),
dev->bulk_in_buffer,
min(dev->bulk_in_size, count),
&bytes_read, 10000);
/* if the read was successful, copy the data to userspace */
if (!retval) {
if (copy_to_user(buffer, dev->bulk_in_buffer, bytes_read))
retval = -EFAULT;
else
retval = bytes_read;
}
return retval;
}
static void skel_write_bulk_callback(struct urb *urb, struct pt_regs *regs)
{
/*
提交urb被主控制器处理后的调用函数，主要反映数据处理的情况。
*/
struct usb_skel *dev;
dev = (struct usb_skel *)urb->context;
/* sync/async unlink faults aren't errors */
if (urb->status &&
!(urb->status == -ENOENT ||
urb->status == -ECONNRESET ||
urb->status == -ESHUTDOWN)) {
dbg("%s - nonzero write bulk status received: %d",
__FUNCTION__, urb->status);
}
/* free up our allocated buffer */
usb_buffer_free(urb->dev, urb->transfer_buffer_length,
urb->transfer_buffer, urb->transfer_dma);
up(&dev->limit_sem);
}
tatic ssize_t skel_write(struct file *file, const char *user_buffer, size_t count, loff_t *ppos)
{
/*
1.写数据到设备文件的函数，首先要通过文件句柄，得到句柄所指向的设备文件，即我们在probe函数中注册的设备文件。
2.通过文件句柄，可以获得设备的文件操作集，这个操作集一般放在private_data这个指针所指向的位置。
3.分配urb空间
4.分配用户数据空间大小的内核空间，用于接收用户数据
5.填充urb跟发送数据的关系
6.提交urb数据
7.根据提交的返回信息，判断是否正常发送
*/
struct usb_skel *dev;
int retval = 0;
struct urb *urb = NULL;
char *buf = NULL;
size_t writesize = min(count, (size_t)MAX_TRANSFER);
dev = (struct usb_skel *)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 (down_interruptible(&dev->limit_sem)) {
retval = -ERESTARTSYS;
goto exit;
}
/* 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_buffer_alloc(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;
}
/* 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;
/* send the data out the bulk port */
retval = usb_submit_urb(urb, GFP_KERNEL);
if (retval) {
err("%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);
exit:
return writesize;
error:
usb_buffer_free(dev->udev, writesize, buf, urb->transfer_dma);
usb_free_urb(urb);
up(&dev->limit_sem);
return retval;
}
static struct file_operations skel_fops = {
.owner = THIS_MODULE,
.read = skel_read,
.write = skel_write,
.open = skel_open,
.release = skel_release,
};
/*
* 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)
{
/*
probe函数主要完成以下工作:
1.分配一个设备驱动空间，并对这个设备进行引用计数
2.设备空间中的usb device,interface两个成员，分别由真实成员来赋值，目的是把这些真实成员跟这个新的设备空间关联起来
3.判断接口所包含的端点特性，看跟硬件是否一致，如果不一致，则出错，即返回值不等于0
4.注册一个文件设备，这个文件设备是提供给应用程序用于操作设备的，包含打开，关闭，读，写等功能。
5.成功则返回0
*/
struct usb_skel *dev = NULL;
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 == NULL) {
err("Out of memory");
goto error;
}
kref_init(&dev->kref);
sema_init(&dev->limit_sem, WRITES_IN_FLIGHT);
dev->udev = usb_get_dev(interface_to_usbdev(interface));/*通过设备的接口，获得这个接口所对应的设备，并增加设备的引用次数*/
dev->interface = interface;
/* 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 &&
((endpoint->bEndpointAddress & USB_ENDPOINT_DIR_MASK)
== USB_DIR_IN) &&
((endpoint->bmAttributes & USB_ENDPOINT_XFERTYPE_MASK)
== USB_ENDPOINT_XFER_BULK)) {
/* 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;
}
}
if (!dev->bulk_out_endpointAddr &&
((endpoint->bEndpointAddress & USB_ENDPOINT_DIR_MASK)
== USB_DIR_OUT) &&
((endpoint->bmAttributes & USB_ENDPOINT_XFERTYPE_MASK)
== USB_ENDPOINT_XFER_BULK)) {
/* 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 */
info("USB Skeleton device now attached to USBSkel-%d", interface->minor);
return 0;
error:
if (dev)
kref_put(&dev->kref, skel_delete);
return retval;
}
static void skel_disconnect(struct usb_interface *interface)
{
struct usb_skel *dev;
int minor = interface->minor;
/* prevent skel_open() from racing skel_disconnect() */
lock_kernel();
dev = usb_get_intfdata(interface);
usb_set_intfdata(interface, NULL);
/* give back our minor */
usb_deregister_dev(interface, &skel_class);
unlock_kernel();
/* decrement our usage count */
kref_put(&dev->kref, skel_delete);
info("USB Skeleton #%d now disconnected", minor);
}
static struct usb_driver skel_driver = {
.name = "skeleton",
.probe = skel_probe,
.disconnect = skel_disconnect,
.id_table = skel_table,
};
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");
