linux uvc深刻理解(二)

整個uvc驅動，在內核中的路徑是drivers/media/video/uvc
在kernel中配置uvc驅動，須要本身手動在make menuconfig中勾選以下路徑：

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

咱們先用tree看戲uvc目錄下的文件組成：

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

那咱們就先從uvc_driver.c開始剖析整個uvc驅動的架構
首先咱們找到驅動的加載入口module_init宏定義的函數：

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);

加載函數很簡單，除了必要的初始化外，最重要的兩步操做就是：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);
}

這裏面將uvc支持的GUID（即uvc支持的操做選項，包括亮度調節、灰度調節....）
struct uvc_control_info添加到uvc_driver的controls這個隊列中去，其中主要關注這個結構體便可：

struct uvc_control_info {
struct list_head list;
struct list_head mappings;----->添加結構體成員類型struct uvc_control_mapping

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

__u16 size;
__u32 flags;
};

usb_register:

 
這是註冊uvc驅動的接口，就是將

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
},
};

這個結構體註冊到usb驅動中，其中uvc_ids就是usb的過濾器，只有將支持uvc camera的VID和PID填入這個結構體，usb驅動纔會在識別到camera後將其分發給uvc驅動，固然在uvc_ids中最後有這麼個賦值：
/* Generic USB Video Class */
{ USB_INTERFACE_INFO(USB_CLASS_VIDEO, 1, 0) },
也即只要usb描述符中說明是USB_CLASS_VIDEO的，都會交由uvc處理，沒必要單獨將其VID和PID填入了。