linux uvc深刻理解(二)

整个uvc驱动，在内核中的路径是drivers/media/video/uvc
在kernel中配置uvc驱动，须要本身手动在make menuconfig中勾选以下路径：

Device Drivers ---> Multimedia support ---> Video For Linux
Device Drivers ---> Multimedia support ---> [*] Video capture adapters ---> [*] V4L USB devices ---> USB Video Class (UVC)

咱们先用tree看戏uvc目录下的文件组成：

guanguojin@WX-ASIC-S02-Android:uvc$ tree
.
├── Kconfig
├── Makefile
├── uvc_ctrl.c
├── uvc_driver.c //uvc驱动的入口处
├── uvc_isight.c
├── uvc_queue.c
├── uvc_status.c
├── uvc_v4l2.c
├── uvc_video.c
└── uvcvideo.h

那咱们就先从uvc_driver.c开始剖析整个uvc驱动的架构
首先咱们找到驱动的加载入口module_init宏定义的函数：

static int __init uvc_init(void)
{
int result;

INIT_LIST_HEAD(&uvc_driver.devices);
INIT_LIST_HEAD(&uvc_driver.controls);
mutex_init(&uvc_driver.ctrl_mutex);

uvc_ctrl_init();

result = usb_register(&uvc_driver.driver);
if (result == 0)
printk(KERN_INFO DRIVER_DESC " (" DRIVER_VERSION ")\n");
return result;
}
module_init(uvc_init);

加载函数很简单，除了必要的初始化外，最重要的两步操做就是：uvc_ctrl_init和usb_register

uvc_ctrl_init

void uvc_ctrl_init(void)
{
struct uvc_control_info *ctrl = uvc_ctrls;
struct uvc_control_info *cend = ctrl + ARRAY_SIZE(uvc_ctrls);
struct uvc_control_mapping *mapping = uvc_ctrl_mappings;
struct uvc_control_mapping *mend =
mapping + ARRAY_SIZE(uvc_ctrl_mappings);

for (; ctrl < cend; ++ctrl)
uvc_ctrl_add_info(ctrl);

for (; mapping < mend; ++mapping)
uvc_ctrl_add_mapping(mapping);
}

这里面将uvc支持的GUID（即uvc支持的操做选项，包括亮度调节、灰度调节....）
struct uvc_control_info添加到uvc_driver的controls这个队列中去，其中主要关注这个结构体便可：

struct uvc_control_info {
struct list_head list;
struct list_head mappings;----->添加结构体成员类型struct uvc_control_mapping

__u8 entity[16];
__u8 index;
__u8 selector;

__u16 size;
__u32 flags;
};

usb_register:

 
这是注册uvc驱动的接口，就是将

struct uvc_driver uvc_driver = {
.driver = {
.name = "uvcvideo",
.probe = uvc_probe,
.disconnect = uvc_disconnect,
.suspend = uvc_suspend,
.resume = uvc_resume,
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 23)
.reset_resume = uvc_reset_resume,
#endif
.id_table = uvc_ids,
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 19)
.supports_autosuspend = 1,
#endif
},
};

这个结构体注册到usb驱动中，其中uvc_ids就是usb的过滤器，只有将支持uvc camera的VID和PID填入这个结构体，usb驱动才会在识别到camera后将其分发给uvc驱动，固然在uvc_ids中最后有这么个赋值：
/* Generic USB Video Class */
{ USB_INTERFACE_INFO(USB_CLASS_VIDEO, 1, 0) },
也即只要usb描述符中说明是USB_CLASS_VIDEO的，都会交由uvc处理，没必要单独将其VID和PID填入了。