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uvc摄像头代码解析6

10.扫描视频设备链和注册视频设备
10.1 uvc视频链
[cpp]  
struct uvc_video_chain {    //uvc视频链  
    struct uvc_device *dev;         //uvc设备  
    struct list_head list;          //uvc视频链链表头  
    struct list_head entities;      //uvc实体链表头  
    struct uvc_entity *processing;  //处理Unit实体  
    struct uvc_entity *selector;    //选择器Unit实体  
    struct mutex ctrl_mutex;        /* Protects ctrl.info */  
};  
10.2 uvc扫描设备
[cpp]  
static int uvc_scan_device(struct uvc_device *dev)  
{  
    struct uvc_video_chain *chain;  //uvc视频链  
    struct uvc_entity *term;    //uvc实体  
  
    list_for_each_entry(term, &dev->entities, list) {    //遍历全局实体链表  
        if (!UVC_ENTITY_IS_OTERM(term)) //获取实体链表中的输出Terminal实体  
            continue;  
        if (term->chain.next || term->chain.prev) //已经添加到uvc视频链中了  
            continue;  
        chain = kzalloc(sizeof(*chain), GFP_KERNEL);    //分配uvc视频链内存(有多少个输入Terminal就有多少个uvc_video_chain)  
        if (chain == NULL)  
            return -ENOMEM;  
        INIT_LIST_HEAD(&chain->entities);    //初始化视频链entities(实体)链表  
        mutex_init(&chain->ctrl_mutex);  
        chain->dev = dev;    //易做图uvc视频链和uvc设备  
        if (uvc_scan_chain(chain, term) < 0) {   //扫描uvc视频链(处理所有相关的输入pin)  
            kfree(chain);  
            continue;  
        }  
        uvc_trace(UVC_TRACE_PROBE, "Found a valid video chain (%s).\n",uvc_print_chain(chain));  
        list_add_tail(&chain->list, &dev->chains);    //添加到uvc设备的uvc视频链链表  
    }  
    if (list_empty(&dev->chains)) {  
        uvc_printk(KERN_INFO, "No valid video chain found.\n");  
        return -1;  
    }  
    return 0;  
}  
10.3 uvc扫描视频链
[cpp]  
static int uvc_scan_chain(struct uvc_video_chain *chain,struct uvc_entity *term)  
{  
    struct uvc_entity *entity, *prev;  
    uvc_trace(UVC_TRACE_PROBE, "Scanning UVC chain:");  
    entity = term;  //获取实体  
    prev = NULL;    //前一个实体  
    while (entity != NULL) {  
        /* Entity must not be part of an existing chain */  
        if (entity->chain.next || entity->chain.prev) {   //已经添加到uvc视频链中了  
            uvc_trace(UVC_TRACE_DESCR, "Found reference to entity %d already in chain.\n", entity->id);  
            return -EINVAL;  
        }  
        /* Process entity */  
        if (uvc_scan_chain_entity(chain, entity) < 0)    //扫描当前实体  
            return -EINVAL;  
        /* Forward scan */  
        if (uvc_scan_chain_forward(chain, entity, prev) < 0) //向前扫描实体  
            return -EINVAL;  
        /* Backward scan */  
        prev = entity;      //当前实体作为下一次while循环的前一个实体  
        if (uvc_scan_chain_backward(chain, &entity) < 0) //向后扫描实体  
            return -EINVAL;  
    }  
    return 0;  
}  
将uvc视频链的输入实体添加到uvc视频链的entities链表中
将uvc视频链添加到uvc设备的chains链表中
10.3.1 扫描当前实体
[cpp]  
static int uvc_scan_chain_entity(struct uvc_video_chain *chain,struct uvc_entity *entity)  
{  
    switch (UVC_ENTITY_TYPE(entity)) {  
    case UVC_VC_EXTENSION_UNIT: //扩展Unit  
        if (uvc_trace_param & UVC_TRACE_PROBE)  
            printk(" <- XU %d", entity->id);  
        if (entity->bNrInPins != 1) {  
            uvc_trace(UVC_TRACE_DESCR, "Extension unit %d has more than 1 input pin.\n", entity->id);  
            return -1;  
        }  
        break;  
    case UVC_VC_PROCESSING_UNIT:    //处理Unit  
        if (uvc_trace_param & UVC_TRACE_PROBE)  
            printk(" <- PU %d", entity->id);  
        if (chain->processing != NULL) {  
            uvc_trace(UVC_TRACE_DESCR, "Found multiple Processing Units in chain.\n");  
            return -1;  
        }  
        chain->processing = entity;  //如果是处理Unit则设置其为uvc视频链的processing对象  
        break;  
    case UVC_VC_SELECTOR_UNIT:  //选择器Unit  
        if (uvc_trace_param & UVC_TRACE_PROBE)  
            printk(" <- SU %d", entity->id);  
        /* Single-input selector units are ignored. */  
        if (entity->bNrInPins == 1)  
            break;  
        if (chain->selector != NULL) {  
            uvc_trace(UVC_TRACE_DESCR, "Found multiple Selector Units in chain.\n");  
            return -1;  
        }  
        chain-&
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