前面的博客已經分析了USB攝像頭驅動程序的框架，我們知道了USB攝像頭驅動程序的重點在於1）描述符的分析；2）屬性的控制（通過VC來設置）；3）格式的選擇（通過VS來設置）；4）數據的獲得（通過VS的URB來獲得）。后面的博客就會從這4個方面進行深入的分析，本篇博客首先來看一下UVC驅動程序的描述符分析。
回顧之前的內容https://www.cnblogs.com/-glb/p/11568992.html，每一個USB設備都有一個設備描述符，設備描述符中有配置描述符，配置描述符中有接口描述符，接口描述符中有端點描述符。
在進行分析之前，首先來看一張USB攝像頭的描述符的布局
白色的描述符是每個usb設備都要支持的，灰色的部分是UVC規范自己定義的。本篇博客將圍繞這張圖進行講解，將圖中的描述符打印出來，來個直觀的感受。
1.史上最簡單的USB攝像頭驅動程序
Myuvc.c
#include <linux/atomic.h> #include <linux/kernel.h> #include <linux/list.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/usb.h> #include <linux/videodev2.h> #include <linux/vmalloc.h> #include <linux/wait.h> #include <linux/version.h> #include <asm/unaligned.h> #include <media/v4l2-common.h>
static int myuvc_probe(struct usb_interface *intf, const struct usb_device_id *id) { static int cnt = 0; printk("myuvc_probe : cnt \n", cnt++); return 0; } static void myuvc_disconnect(struct usb_interface *intf) { static int cnt = 0; printk("myuvc_probe : cnt \n", cnt++); } static struct usb_device_id myuvc_ids[] = { /* Generic USB Video Class */ { USB_INTERFACE_INFO(USB_CLASS_VIDEO, 1, 0) }, {} }; /*1.分配一個usb driver結構體*/
static struct usb_driver myuvc_driver = { .name = "myuvc", .probe = myuvc_probe, .disconnect = myuvc_disconnect, .id_table = myuvc_ids, }; /*2.設置*/
static int myuvc_init(void) { /*3.注冊*/ usb_register(&myuvc_driver); } static void myuvc_exit(void) { usb_deregister(&myuvc_driver); } module_init(myuvc_init); module_exit(myuvc_exit); MODULE_LICENSE("GPL v2");
1.1分析USB_INTERFACE_INFO(USB_CLASS_VIDEO, 1, 0)
USB_INTERFACE_INFO是一個宏，首先看一下該宏是如何定義的：
#define USB_INTERFACE_INFO(cl, sc, pr) \ .match_flags = USB_DEVICE_ID_MATCH_INT_INFO, \ .bInterfaceClass = (cl), \ .bInterfaceSubClass = (sc), \ .bInterfaceProtocol = (pr)
第一個參數cl：表示Video interface class
第二個參數sc：表示Video interface subclass
第三個參數pr：表示Video interface protocol
#define USB_CLASS_VIDEO 0x0e
任意一個USB攝像頭，它都有一個視頻控制接口，在這個地方為什么不把視頻流接口也放上去呢？
因為只要硬件上有視頻控制接口，就可以根據視頻控制接口找到從屬於此視頻控制接口的視頻流接口。
上面這個驅動程序沒有實際的意義，只是當我們插上USB攝像頭的時候，會將USB攝像頭的接口個數進行打印。在程序中，我們只有一個視頻控制接口，所有cnt的值為1.
注意：在進行試驗的時候，首先將ubuntu中自帶的USB攝像頭驅動程序去掉，然后安裝上我們自己編寫的USB攝像頭驅動程序。
2. 打印設備描述符
lsusb Bus 001 Device 007: ID 1e4e: 0102 Bus 001 Device 007: ID 1d6b: 0002 Linux Foundation 2.0 root hub Bus 001 Device 007: ID 1e4e: 0001 Linux Foundation 1.1 root hub
lsusb.c: main dumpdev dump_device dump_config for (i = 0 ; i < config->bNumInterfaces ; i++) dump_interface(dev, &config->interface[i]); for (i = 0; i < interface->num_altsetting; i++) dump_altsetting(dev, &interface->altsetting[i]);
#include <linux/atomic.h> #include <linux/kernel.h> #include <linux/list.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/usb.h> #include <linux/videodev2.h> #include <linux/vmalloc.h> #include <linux/wait.h> #include <linux/version.h> #include <asm/unaligned.h> #include <media/v4l2-common.h> static int myuvc_probe(struct usb_interface *intf, const struct usb_device_id *id) { static int cnt = 0; struct usb_device *udev = interface_to_usbdev(intf); struct usb_device_descriptor *descriptor = &dev->descriptor; printk("myuvc_probe : cnt \n", cnt++); /* 打印設備描述符 */ printk("Device Descriptor:\n" " bLength %5u\n" " bDescriptorType %5u\n" " bcdUSB %2x.%02x\n" " bDeviceClass %5u \n" " bDeviceSubClass %5u \n" " bDeviceProtocol %5u \n" " bMaxPacketSize0 %5u\n" " idVendor 0x%04x \n" " idProduct 0x%04x \n" " bcdDevice %2x.%02x\n" " iManufacturer %5u\n" " iProduct %5u\n" " iSerial %5u\n" " bNumConfigurations %5u\n", descriptor->bLength, descriptor->bDescriptorType, descriptor->bcdUSB >> 8, descriptor->bcdUSB & 0xff, descriptor->bDeviceClass, descriptor->bDeviceSubClass, descriptor->bDeviceProtocol, descriptor->bMaxPacketSize0, descriptor->idVendor, descriptor->idProduct, descriptor->bcdDevice >> 8, descriptor->bcdDevice & 0xff, descriptor->iManufacturer, descriptor->iProduct, descriptor->iSerialNumber, descriptor->bNumConfigurations); return 0; } static void myuvc_disconnect(struct usb_interface *intf) { static int cnt = 0; printk("myuvc_probe : cnt \n", cnt++); } static struct usb_device_id myuvc_ids[] = { /* Generic USB Video Class */ { USB_INTERFACE_INFO(USB_CLASS_VIDEO, 1, 0) }, {} }; /*1.分配一個usb driver結構體*/ static struct usb_driver myuvc_driver = { .name = "myuvc", .probe = myuvc_probe, .disconnect = myuvc_disconnect, .id_table = myuvc_ids, }; /*2.設置*/ static int myuvc_init(void) { /*3.注冊*/ usb_register(&myuvc_driver); } static void myuvc_exit(void) { usb_deregister(&myuvc_driver); } module_init(myuvc_init); module_exit(myuvc_exit); MODULE_LICENSE("GPL v2");
3. 打印配置描述符
#include <linux/atomic.h> #include <linux/kernel.h> #include <linux/list.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/usb.h> #include <linux/videodev2.h> #include <linux/vmalloc.h> #include <linux/wait.h> #include <linux/version.h> #include <asm/unaligned.h> #include <media/v4l2-common.h> static int myuvc_probe(struct usb_interface *intf, const struct usb_device_id *id) { static int cnt = 0; struct usb_device *udev = interface_to_usbdev(intf); struct usb_device_descriptor *descriptor = &dev->descriptor; struct usb_host_config *hostconfig; struct usb_config_descriptor *config; int i = 0; printk("myuvc_probe : cnt \n", cnt++); /* 打印設備描述符 */ printk("Device Descriptor:\n" " bLength %5u\n" " bDescriptorType %5u\n" " bcdUSB %2x.%02x\n" " bDeviceClass %5u \n" " bDeviceSubClass %5u \n" " bDeviceProtocol %5u \n" " bMaxPacketSize0 %5u\n" " idVendor 0x%04x \n" " idProduct 0x%04x \n" " bcdDevice %2x.%02x\n" " iManufacturer %5u\n" " iProduct %5u\n" " iSerial %5u\n" " bNumConfigurations %5u\n", descriptor->bLength, descriptor->bDescriptorType, descriptor->bcdUSB >> 8, descriptor->bcdUSB & 0xff, descriptor->bDeviceClass, descriptor->bDeviceSubClass, descriptor->bDeviceProtocol, descriptor->bMaxPacketSize0, descriptor->idVendor, descriptor->idProduct, descriptor->bcdDevice >> 8, descriptor->bcdDevice & 0xff, descriptor->iManufacturer, descriptor->iProduct, descriptor->iSerialNumber, descriptor->bNumConfigurations); for (i = 0; i < descriptor->bNumConfigurations; i++) { hostconfig = &dev->config[i]; config = &hostconfig->desc; printk(" Configuration Descriptor %d:\n" " bLength %5u\n" " bDescriptorType %5u\n" " wTotalLength %5u\n" " bNumInterfaces %5u\n" " bConfigurationValue %5u\n" " iConfiguration %5u\n" " bmAttributes 0x%02x\n", i, config->bLength, config->bDescriptorType, le16_to_cpu(config->wTotalLength), config->bNumInterfaces, config->bConfigurationValue, config->iConfiguration, config->bmAttributes); } return 0; } static void myuvc_disconnect(struct usb_interface *intf) { static int cnt = 0; printk("myuvc_probe : cnt \n", cnt++); } static struct usb_device_id myuvc_ids[] = { /* Generic USB Video Class */ { USB_INTERFACE_INFO(USB_CLASS_VIDEO, 1, 0) }, {} }; /*1.分配一個usb driver結構體*/ static struct usb_driver myuvc_driver = { .name = "myuvc", .probe = myuvc_probe, .disconnect = myuvc_disconnect, .id_table = myuvc_ids, }; /*2.設置*/ static int myuvc_init(void) { /*3.注冊*/ usb_register(&myuvc_driver); } static void myuvc_exit(void) { usb_deregister(&myuvc_driver); } module_init(myuvc_init); module_exit(myuvc_exit); MODULE_LICENSE("GPL v2");
4.打印配置描述符中的第一個接口描述符
#include <linux/kernel.h> #include <linux/list.h> #include <linux/module.h> #include <linux/usb.h> #include <linux/videodev2.h> #include <linux/vmalloc.h> #include <linux/wait.h> #include <asm/atomic.h> #include <asm/unaligned.h> #include <media/v4l2-common.h> static int myuvc_probe(struct usb_interface *intf, const struct usb_device_id *id) { static int cnt = 0; struct usb_device *dev = interface_to_usbdev(intf); struct usb_device_descriptor *descriptor = &dev->descriptor; struct usb_host_config *hostconfig; struct usb_config_descriptor *config; struct usb_interface_assoc_descriptor *assoc_desc; int i; printk("myuvc_probe : cnt = %d\n", cnt++); /* 打印設備描述符 */ printk("Device Descriptor:\n" " bLength %5u\n" " bDescriptorType %5u\n" " bcdUSB %2x.%02x\n" " bDeviceClass %5u \n" " bDeviceSubClass %5u \n" " bDeviceProtocol %5u \n" " bMaxPacketSize0 %5u\n" " idVendor 0x%04x \n" " idProduct 0x%04x \n" " bcdDevice %2x.%02x\n" " iManufacturer %5u\n" " iProduct %5u\n" " iSerial %5u\n" " bNumConfigurations %5u\n", descriptor->bLength, descriptor->bDescriptorType, descriptor->bcdUSB >> 8, descriptor->bcdUSB & 0xff, descriptor->bDeviceClass, descriptor->bDeviceSubClass, descriptor->bDeviceProtocol, descriptor->bMaxPacketSize0, descriptor->idVendor, descriptor->idProduct, descriptor->bcdDevice >> 8, descriptor->bcdDevice & 0xff, descriptor->iManufacturer, descriptor->iProduct, descriptor->iSerialNumber, descriptor->bNumConfigurations); for (i = 0; i < descriptor->bNumConfigurations; i++) { hostconfig = &dev->config[i]; config = &hostconfig->desc; printk(" Configuration Descriptor %d:\n" " bLength %5u\n" " bDescriptorType %5u\n" " wTotalLength %5u\n" " bNumInterfaces %5u\n" " bConfigurationValue %5u\n" " iConfiguration %5u\n" " bmAttributes 0x%02x\n", i, config->bLength, config->bDescriptorType, le16_to_cpu(config->wTotalLength), config->bNumInterfaces, config->bConfigurationValue, config->iConfiguration, config->bmAttributes); assoc_desc = hostconfig->intf_assoc[0]; printk(" Interface Association:\n" " bLength %5u\n" " bDescriptorType %5u\n" " bFirstInterface %5u\n" " bInterfaceCount %5u\n" " bFunctionClass %5u\n" " bFunctionSubClass %5u\n" " bFunctionProtocol %5u\n" " iFunction %5u\n", assoc_desc->bLength, assoc_desc->bDescriptorType, assoc_desc->bFirstInterface, assoc_desc->bInterfaceCount, assoc_desc->bFunctionClass, assoc_desc->bFunctionSubClass, assoc_desc->bFunctionProtocol, assoc_desc->iFunction); } return 0; } static void myuvc_disconnect(struct usb_interface *intf) { static int cnt = 0; printk("myuvc_disconnect : cnt = %d\n", cnt++); } static struct usb_device_id myuvc_ids[] = { /* Generic USB Video Class */ { USB_INTERFACE_INFO(USB_CLASS_VIDEO, 1, 0) }, /* VideoControl Interface */ { USB_INTERFACE_INFO(USB_CLASS_VIDEO, 2, 0) }, /* VideoStreaming Interface */ {} }; /* 1. 分配usb_driver */ /* 2. 設置 */ static struct usb_driver myuvc_driver = { .name = "myuvc", .probe = myuvc_probe, .disconnect = myuvc_disconnect, .id_table = myuvc_ids, }; static int myuvc_init(void) { /* 3. 注冊 */ usb_register(&myuvc_driver); return 0; } static void myuvc_exit(void) { usb_deregister(&myuvc_driver); } module_init(myuvc_init); module_exit(myuvc_exit); MODULE_LICENSE("GPL");
5.打印接口描述符
在probe函數中，參數就有接口這一項，usb設備中有多個接口，如果這個接口能被driver所支持，即吻合id_table的話，該接口就會作為一個參數傳給probe函數。
在一個接口中可能有多個設置，用struct usb_host_interface *altsetting來表示；當前使用哪個設置呢？使用struct usb_host_interface *cur_altsetting; /* the currently來表示。
#include <linux/kernel.h> #include <linux/list.h> #include <linux/module.h> #include <linux/usb.h> #include <linux/videodev2.h> #include <linux/vmalloc.h> #include <linux/wait.h> #include <asm/atomic.h> #include <asm/unaligned.h> #include <media/v4l2-common.h> static int myuvc_probe(struct usb_interface *intf, const struct usb_device_id *id) { static int cnt = 0; struct usb_device *dev = interface_to_usbdev(intf); struct usb_device_descriptor *descriptor = &dev->descriptor; struct usb_host_config *hostconfig; struct usb_config_descriptor *config; struct usb_interface_assoc_descriptor *assoc_desc; struct usb_interface_descriptor *interface; int i, j; printk("myuvc_probe : cnt = %d\n", cnt++); /* 打印設備描述符 */ printk("Device Descriptor:\n" " bLength %5u\n" " bDescriptorType %5u\n" " bcdUSB %2x.%02x\n" " bDeviceClass %5u \n" " bDeviceSubClass %5u \n" " bDeviceProtocol %5u \n" " bMaxPacketSize0 %5u\n" " idVendor 0x%04x \n" " idProduct 0x%04x \n" " bcdDevice %2x.%02x\n" " iManufacturer %5u\n" " iProduct %5u\n" " iSerial %5u\n" " bNumConfigurations %5u\n", descriptor->bLength, descriptor->bDescriptorType, descriptor->bcdUSB >> 8, descriptor->bcdUSB & 0xff, descriptor->bDeviceClass, descriptor->bDeviceSubClass, descriptor->bDeviceProtocol, descriptor->bMaxPacketSize0, descriptor->idVendor, descriptor->idProduct, descriptor->bcdDevice >> 8, descriptor->bcdDevice & 0xff, descriptor->iManufacturer, descriptor->iProduct, descriptor->iSerialNumber, descriptor->bNumConfigurations); for (i = 0; i < descriptor->bNumConfigurations; i++) { hostconfig = &dev->config[i]; config = &hostconfig->desc; printk(" Configuration Descriptor %d:\n" " bLength %5u\n" " bDescriptorType %5u\n" " wTotalLength %5u\n" " bNumInterfaces %5u\n" " bConfigurationValue %5u\n" " iConfiguration %5u\n" " bmAttributes 0x%02x\n", i, config->bLength, config->bDescriptorType, le16_to_cpu(config->wTotalLength), config->bNumInterfaces, config->bConfigurationValue, config->iConfiguration, config->bmAttributes); assoc_desc = hostconfig->intf_assoc[0]; printk(" Interface Association:\n" " bLength %5u\n" " bDescriptorType %5u\n" " bFirstInterface %5u\n" " bInterfaceCount %5u\n" " bFunctionClass %5u\n" " bFunctionSubClass %5u\n" " bFunctionProtocol %5u\n" " iFunction %5u\n", assoc_desc->bLength, assoc_desc->bDescriptorType, assoc_desc->bFirstInterface, assoc_desc->bInterfaceCount, assoc_desc->bFunctionClass, assoc_desc->bFunctionSubClass, assoc_desc->bFunctionProtocol, assoc_desc->iFunction); for (j = 0; j < intf->num_altsetting; j++) { interface = &intf->altsetting[j].desc; printk(" Interface Descriptor altsetting %d:\n" " bLength %5u\n" " bDescriptorType %5u\n" " bInterfaceNumber %5u\n" " bAlternateSetting %5u\n" " bNumEndpoints %5u\n" " bInterfaceClass %5u\n" " bInterfaceSubClass %5u\n" " bInterfaceProtocol %5u\n" " iInterface %5u\n", j, interface->bLength, interface->bDescriptorType, interface->bInterfaceNumber, interface->bAlternateSetting, interface->bNumEndpoints, interface->bInterfaceClass, interface->bInterfaceSubClass, interface->bInterfaceProtocol, interface->iInterface); } } return 0; } static void myuvc_disconnect(struct usb_interface *intf) { static int cnt = 0; printk("myuvc_disconnect : cnt = %d\n", cnt++); } static struct usb_device_id myuvc_ids[] = { /* Generic USB Video Class */ { USB_INTERFACE_INFO(USB_CLASS_VIDEO, 1, 0) }, /* VideoControl Interface */ { USB_INTERFACE_INFO(USB_CLASS_VIDEO, 2, 0) }, /* VideoStreaming Interface */ {} }; /* 1. 分配usb_driver */ /* 2. 設置 */ static struct usb_driver myuvc_driver = { .name = "myuvc", .probe = myuvc_probe, .disconnect = myuvc_disconnect, .id_table = myuvc_ids, }; static int myuvc_init(void) { /* 3. 注冊 */ usb_register(&myuvc_driver); return 0; } static void myuvc_exit(void) { usb_deregister(&myuvc_driver); } module_init(myuvc_init); module_exit(myuvc_exit); MODULE_LICENSE("GPL");
6. 打印UVC規范定義的描述符
UVC規范中定義的描述符，有輸入描述符、處理單元描述符、選擇單元描述符、輸出單元描述符等，這些描述符存在某個buffer中，即當前設置里面有個buffer。
打印結果如下所示：
VideoControl Interface的自定義描述符：
VideoStreaming Interface的自定義描述符：
下篇博客將對buffer中打印的這些信息進行詳細的介紹。