ATK-IMX6U 阿尔法i.MX6ULL · 内核 4.1.15× 杂牌 USB 摄像头VID:PID 4a54:52321. 问题现象USB 摄像头插上开发板 USB Host 口后内核日志报错摄像头节点没有创建[ 214.596875] usb 1-1: new high-speed USB device number 2 using ci_hdrc [ 214.836067] uvcvideo: Found UVC 1.00 device unnamed (4a54:5232) [ 214.849918] input: UVC Camera (4a54:5232) as /devices/platform/soc/2184000.usb/ci_hdrc.1/usb1/1-1/1-1:1.0/input/input2 [ 214.911655] uvcvideo: No valid video chain found.关键信息USB 枚举成功、uvcvideo 驱动也成功加载并认出了设备Found UVC 1.00 device但最后一句No valid video chain found.导致注册失败、节点不出现。2. 排查过程2.1 排除硬件问题alientekubuntu16:~$ lsusb Bus 001 Device 003: ID 4a54:5232 # 同一设备 alientekubuntu16:~$ ls /dev/video* # 虚拟机上正常出现 /dev/video0可打开预览结论摄像头硬件没问题是板端驱动适配失败。2.2 确认内核 UVC 驱动的配置形态rootalientek:~# lsmod | grep uvc uvcvideo 79519 0 videobuf2_vmalloc 3483 1 uvcvideo可以重新编译ko文件替换即可。2.3 定位报错来源在内核源码drivers/media/usb/uvc/uvc_driver.c中搜索报错字符串找到打印位置static int uvc_scan_device(struct uvc_device *dev) { ... if (list_empty(dev-chains)) { // 所有视频链扫描全部失败 uvc_printk(KERN_INFO, No valid video chain found.\n); return -1; }调用链uvc_scan_device()对每个输出终端调用uvc_scan_chain() 后者沿baSourceID逐级向上回溯uvc_scan_chain_backward 输出终端 OT → 处理单元 PU / 扩展单元 XU → 输入终端 IT。任何一环的 ID 指向不存在的实体整条链即告失败。3. 原因分析摄像头固件的 UVC 描述符链断裂查上游内核邮件列表发现正是这类问题有官方补丁commit e950267ab802c8558f1100eafd4087fd039ad634 Author: Henrik Ingo henrik.ingoavoinelama.fi Date: Sun May 29 17:58:00 2016 -0300 [media] uvcvideo: uvc_scan_fallback() for webcams with broken chain Some devices have invalid baSourceID references, causing uvc_scan_chain() to fail, but if we just take the entities we can find and put them together in the most sensible chain we can think of, turns out they do work anyway. Note: This heuristic assumes there is a single chain. At the time of writing, devices known to have such a broken chain are - Acer Integrated Camera (5986:055a) - Realtek rtl157a7 (0bda:57a7)补丁思想标准扫描失败后不再要求描述符链完整而是把能找到的实体按最合理的顺序手工串成一条链OT ← PU/XU 按序 ← IT并顺手修正错误的 baSourceID。4a54:5232 属于同一类固件缺陷直接套用此补丁。4. 修改drivers/media/usb/uvc/uvc_driver.cstatic struct uvc_video_chain *uvc_alloc_chain(struct uvc_device *dev) { struct uvc_video_chain *chain; chain kzalloc(sizeof(*chain), GFP_KERNEL); if (chain NULL) return NULL; INIT_LIST_HEAD(chain-entities); mutex_init(chain-ctrl_mutex); chain-dev dev; v4l2_prio_init(chain-prio); return chain; } static int uvc_scan_fallback(struct uvc_device *dev) { struct uvc_video_chain *chain; struct uvc_entity *iterm NULL; struct uvc_entity *oterm NULL; struct uvc_entity *entity; struct uvc_entity *prev; /* 定位输入/输出终端当前仅支持各恰好一个 */ list_for_each_entry(entity, dev-entities, list) { if (UVC_ENTITY_IS_ITERM(entity)) { if (iterm) return -EINVAL; iterm entity; } if (UVC_ENTITY_IS_OTERM(entity)) { if (oterm) return -EINVAL; oterm entity; } } if (iterm NULL || oterm NULL) return -EINVAL; /* 分配链并填充 */ chain uvc_alloc_chain(dev); if (chain NULL) return -ENOMEM; if (uvc_scan_chain_entity(chain, oterm) 0) goto error; prev oterm; /* * 从输出端向输入端构建链按逆序遍历实体表把所有有两个 pad 的 * PU / XU 依次串进来并逐级修正 baSourceID这就是在修固件写错的地方 */ list_for_each_entry_reverse(entity, dev-entities, list) { if (entity-type ! UVC_VC_PROCESSING_UNIT entity-type ! UVC_VC_EXTENSION_UNIT) continue; if (entity-num_pads ! 2) continue; if (uvc_scan_chain_entity(chain, entity) 0) goto error; prev-baSourceID[0] entity-id; prev entity; } if (uvc_scan_chain_entity(chain, iterm) 0) goto error; prev-baSourceID[0] iterm-id; list_add_tail(chain-list, dev-chains); uvc_trace(UVC_TRACE_PROBE, Found a video chain by fallback heuristic (%s).\n, uvc_print_chain(chain)); return 0; error: kfree(chain); return -EINVAL; }改动二uvc_scan_device() 里链的分配改用新函数原代码删除 chain kzalloc(sizeof(*chain), GFP_KERNEL); 及其后的 INIT_LIST_HEAD / mutex_init / chain-dev / v4l2_prio_init 四行初始化 改为一行 chain uvc_alloc_chain(dev);改动三uvc_scan_device() 末尾启用回退扫描list_add_tail(chain-list, dev-chains); } if (list_empty(dev-chains)) uvc_scan_fallback(dev); // 标准扫描全失败 → 启用回退启发式 if (list_empty(dev-chains)) { uvc_printk(KERN_INFO, No valid video chain found.\n); return -1; }5. 编译uvcvideo.ko模块直接在ubuntu虚拟机进入到正点原子释放的kernel内核源码处编译内核。编出的uvcvideo.ko位于drivers/media/usb/uvc/uvcvideo.ko。6. 验证rootalientek:~# rmmod uvcvideo # 卸载旧模块若已加载 rootalientek:~# insmod /mnt/udisk/uvcvideo.ko [ 456.183320] uvcvideo: Found UVC 1.00 device unnamed (4a54:5232) # 注意这次没有再出现 No valid video chain found. —— 回退扫描成功了 rootalientek:~# ls /sys/class/video4linux/ video0 video1 video2 # video2 出现 rootalientek:~# cat /sys/class/video4linux/video2/name Web Camerafbdevsink 直出有画面但卡顿rootalientek:~# gst-launch-1.0 v4l2src device/dev/video2 ! \ image/jpeg,width640,height360,framerate30/1 ! jpegdec ! fbdevsink Setting pipeline to PLAYING ... WARNING: from element /GstPipeline:pipeline0/...: A lot of buffers are being dropped. WARNING: ...持续刷屏i.MX6ULL没有 IPU / VPU 硬件编解码单元MJPEG 软解、格式转换全压在单核 Cortex-A7 上30fps 下 CPU 处理不过来缓冲堆积丢帧。后续会适配到正点原子出场qt上。。。。。。。。。