Linux下的USB总线驱动 mouse

Linux下的USB总线驱动(03)——USB鼠标驱动 usbmouse.c

USB鼠标驱动 usbmouse.c

原文链接：http://www.linuxidc.com/Linux/2012-12/76197p7.htm

drivers/hid/usbhid/usbmouse.c

下面我们分析下USB鼠标驱动，鼠标输入HID类型，其数据传输采用中断URB，鼠标端点类型为IN。我们先看看这个驱动的模块加载部分。

static int __init usb_mouse_init(void)
{
int retval = usb_register(&usb_mouse_driver);
if (retval == 0)
printk(KERN_INFO KBUILD_MODNAME ": " DRIVER_VERSION ":"
DRIVER_DESC "\n");
return retval;
}

模块加载部分仍然是调用usb_register注册USB驱动，我们跟踪看看被注册的usb_mouse_driver

static struct usb_driver usb_mouse_driver = {
.name = "usbmouse", //驱动名
.probe = usb_mouse_probe,
.disconnect = usb_mouse_disconnect,
.id_table = usb_mouse_id_table, //支持项
};

关于设备支持项我们前面已经讨论过了

static struct usb_device_id usb_mouse_id_table [] = {
{ USB_INTERFACE_INFO(USB_INTERFACE_CLASS_HID, USB_INTERFACE_SUBCLASS_BOOT,
USB_INTERFACE_PROTOCOL_MOUSE) },
{ } /* Terminating entry */
};
MODULE_DEVICE_TABLE (usb, usb_mouse_id_table);

再细细看看USB_INTERFACE_INFO宏的定义

/**
* USB_INTERFACE_INFO - macro used to describe a class of usb interfaces
* @cl: bInterfaceClass value
* @sc: bInterfaceSubClass value
* @pr: bInterfaceProtocol value
*
* This macro is used to create a struct usb_device_id that matches a
* specific class of interfaces.
*/
#define USB_INTERFACE_INFO(cl, sc, pr) \
.match_flags = USB_DEVICE_ID_MATCH_INT_INFO, \
.bInterfaceClass = (cl), \
.bInterfaceSubClass = (sc), \
.bInterfaceProtocol = (pr)

根据宏，我们知道，我们设置的支持项包括接口类，接口子类，接口协议三个匹配项。

主要看看usb_driver中定义的probe函数

static int usb_mouse_probe(struct usb_interface *intf, const struct usb_device_id *id)
{
struct usb_device *dev = interface_to_usbdev(intf);//由接口获取usb_dev
struct usb_host_interface *interface;
struct usb_endpoint_descriptor *endpoint;
struct usb_mouse *mouse; //该驱动私有结构体
struct input_dev *input_dev; //输入结构体
int pipe, maxp;
int error = -ENOMEM;
interface = intf->cur_altsetting; //获取设置
if (interface->desc.bNumEndpoints != 1) //鼠标端点只有1个
return -ENODEV;
endpoint = &interface->endpoint[0].desc; //获取端点描述符
if (!usb_endpoint_is_int_in(endpoint)) //检查该端点是否是中断输入端点
return -ENODEV;
pipe = usb_rcvintpipe(dev, endpoint->bEndpointAddress); //建立中断输入端点
maxp = usb_maxpacket(dev, pipe, usb_pipeout(pipe)); //端点能传输的最大数据包(Mouse为4个)
mouse = kzalloc(sizeof(struct usb_mouse), GFP_KERNEL); //分配usb_mouse结构体
input_dev = input_allocate_device(); //分配input设备空间
if (!mouse || !input_dev)
goto fail1;
mouse->data = usb_alloc_coherent(dev, 8, GFP_ATOMIC, &mouse->data_dma); //分配缓冲区
if (!mouse->data)
goto fail1;
mouse->irq = usb_alloc_urb(0, GFP_KERNEL); //分配urb
if (!mouse->irq)
goto fail2;
mouse->usbdev = dev; //填充mouse的usb_device结构体
mouse->dev = input_dev; //填充mouse的input结构体
if (dev->manufacturer) //复制厂商ID
strlcpy(mouse->name, dev->manufacturer, sizeof(mouse->name));
if (dev->product) { //复制产品ID
if (dev->manufacturer)
strlcat(mouse->name, " ", sizeof(mouse->name));
strlcat(mouse->name, dev->product, sizeof(mouse->name));
}
if (!strlen(mouse->name))
snprintf(mouse->name, sizeof(mouse->name),
"USB HIDBP Mouse %04x:%04x",
le16_to_cpu(dev->descriptor.idVendor),
le16_to_cpu(dev->descriptor.idProduct));
usb_make_path(dev, mouse->phys, sizeof(mouse->phys));
strlcat(mouse->phys, "/input0", sizeof(mouse->phys)); //获取usb_mouse的设备节点
input_dev->name = mouse->name; //将鼠标名赋给内嵌input结构体
input_dev->phys = mouse->phys; //将鼠标设备节点名赋给内嵌input结构体
usb_to_input_id(dev, &input_dev->id); //将usb_driver的支持项拷贝给input
input_dev->dev.parent = &intf->dev;
input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REL); //支持按键事件和相对坐标事件
input_dev->keybit[BIT_WORD(BTN_MOUSE)] = BIT_MASK(BTN_LEFT) |
BIT_MASK(BTN_RIGHT) | BIT_MASK(BTN_MIDDLE); //表明按键值包括左键、中键和右键
input_dev->relbit[0] = BIT_MASK(REL_X) | BIT_MASK(REL_Y); //表明相对坐标包括X坐标和Y坐标
input_dev->keybit[BIT_WORD(BTN_MOUSE)] |= BIT_MASK(BTN_SIDE) |
BIT_MASK(BTN_EXTRA); //表明除了左键、右键和中键，还支持其他按键
input_dev->relbit[0] |= BIT_MASK(REL_WHEEL); //表明还支持中键滚轮的滚动值
input_set_drvdata(input_dev, mouse); //将mouse设为input的私有数据
input_dev->open = usb_mouse_open; //input设备的open操作函数
input_dev->close = usb_mouse_close;
usb_fill_int_urb(mouse->irq, dev, pipe, mouse->data,
(maxp > 8 ? 8 : maxp),
usb_mouse_irq, mouse, endpoint->bInterval); //填充urb
mouse->irq->transfer_dma = mouse->data_dma;
mouse->irq->transfer_flags |= URB_NO_TRANSFER_DMA_MAP; //使用transfer_dma
error = input_register_device(mouse->dev); //注册input设备
if (error)
goto fail3;
usb_set_intfdata(intf, mouse);
return 0;
fail3:
usb_free_urb(mouse->irq);
fail2:
usb_free_coherent(dev, 8, mouse->data, mouse->data_dma);
fail1:
input_free_device(input_dev);
kfree(mouse);
return error;
}

在探讨probe实现的功能时，我们先看看urb填充函数usb_fill_int_urb

/**
* usb_fill_int_urb - macro to help initialize a interrupt urb
* @urb: pointer to the urb to initialize.
* @dev: pointer to the struct usb_device for this urb.
* @pipe: the endpoint pipe
* @transfer_buffer: pointer to the transfer buffer
* @buffer_length: length of the transfer buffer
* @complete_fn: pointer to the usb_complete_t function
* @context: what to set the urb context to.
* @interval: what to set the urb interval to, encoded like
* the endpoint descriptor's bInterval value.
*
* Initializes a interrupt urb with the proper information needed to submit
* it to a device.
*
* Note that High Speed and SuperSpeed interrupt endpoints use a logarithmic
* encoding of the endpoint interval, and express polling intervals in
* microframes (eight per millisecond) rather than in frames (one per
* millisecond).
*
* Wireless USB also uses the logarithmic encoding, but specifies it in units of
* 128us instead of 125us. For Wireless USB devices, the interval is passed
* through to the host controller, rather than being translated into microframe
* units.
*/
static inline void usb_fill_int_urb(struct urb *urb,
struct usb_device *dev,
unsigned int pipe,
void *transfer_buffer,
int buffer_length,
usb_complete_t complete_fn,
void *context,
int interval)
{
urb->dev = dev;
urb->pipe = pipe;
urb->transfer_buffer = transfer_buffer;
urb->transfer_buffer_length = buffer_length;
urb->complete = complete_fn;
urb->context = context;
if (dev->speed == USB_SPEED_HIGH || dev->speed == USB_SPEED_SUPER)
urb->interval = 1 << (interval - 1);
else
urb->interval = interval;
urb->start_frame = -1;
}

其实probe主要是初始化usb设备和input设备，终极目标是为了完成urb的提交和input设备的注册。由于注册为input设备类型，那么当用户层open打开设备时候，最终会调用input中的open实现打开，我们看看input中open的实现

static int usb_mouse_open(struct input_dev *dev)
{
struct usb_mouse *mouse = input_get_drvdata(dev); //获取私有数据
mouse->irq->dev = mouse->usbdev; //获取utb指针
if (usb_submit_urb(mouse->irq, GFP_KERNEL)) //提交urb
return -EIO;
return 0;
}

当用户层open打开这个USB鼠标后，我们就已经将urb提交给了USB core，那么根据USB数据处理流程知道，当处理完毕后，USB core会通知USB设备驱动程序，这里我们是响应中断服务程序，这就相当于该URB的回调函数。我们在提交urb时候定义了中断服务程序 usb_mouse_irq，我们跟踪看看

static void usb_mouse_irq(struct urb *urb)
{
struct usb_mouse *mouse = urb->context;
signed char *data = mouse->data;
struct input_dev *dev = mouse->dev;
int status;
switch (urb->status) {
case 0: /* success */
break;
case -ECONNRESET: /* unlink */
case -ENOENT:
case -ESHUTDOWN:
return;
/* -EPIPE: should clear the halt */
default: /* error */
goto resubmit; //数据处理没成功，重新提交urb
}
input_report_key(dev, BTN_LEFT, data[0] & 0x01); //左键
input_report_key(dev, BTN_RIGHT, data[0] & 0x02); //
input_report_key(dev, BTN_MIDDLE, data[0] & 0x04); //
input_report_key(dev, BTN_SIDE, data[0] & 0x08); //
input_report_key(dev, BTN_EXTRA, data[0] & 0x10); //
input_report_rel(dev, REL_X, data[1]); //鼠标的水平位移
input_report_rel(dev, REL_Y, data[2]); //鼠标的垂直位移
input_report_rel(dev, REL_WHEEL, data[3]); //鼠标滚轮的滚动值
input_sync(dev); //同步事件，完成一次上报
resubmit:
status = usb_submit_urb (urb, GFP_ATOMIC); //再次提交urb，等待下次响应
if (status)
err ("can't resubmit intr, %s-%s/input0, status %d",
mouse->usbdev->bus->bus_name,
mouse->usbdev->devpath, status);
}

根据上面的中断服务程序，我们应该知道，系统是周期性地获取鼠标的事件信息，因此在URB回调函数的末尾再次提交URB请求块，这样又会调用新的回调函数，周而复始。在回调函数中提交URB只能是GFP_ATOMIC优先级，因为URB回调函数运行于中断上下文中禁止导致睡眠的行为。而在提交URB 过程中可能会需要申请内存、保持信号量，这些操作或许会导致USB内核睡眠。

最后我们再看看这个驱动的私有数据mouse的定义

struct usb_mouse {
char name[128]; //名字
char phys[64]; //设备节点
struct usb_device *usbdev; //内嵌usb_device设备
struct input_dev *dev; //内嵌input_dev设备
struct urb *irq; //urb结构体
signed char *data; //transfer_buffer缓冲区
dma_addr_t data_dma; //transfer _dma缓冲区
};

在上面这个结构体中，每一个成员的作用都应该很清楚了，尤其最后两个的使用区别和作用，前面也已经说过。

如果最终需要测试这个USB鼠标驱动，需要在内核中配置USB支持、对HID接口的支持、对OHCI HCD驱动的支持。另外，将驱动移植到开发板之后，由于采用的是input设备模型，所以还需要开发板带LCD屏才能测试。

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