UVC框架下USB摄像头驱动之设置属性

1. 在视频驱动程序中设置属性主要涉及3个ioctl ：

VIDIOC_QUERYCTRL
VIDIOC_G_CTRL
VIDIOC_S_CTRL

2. 硬件上怎么设置属性呢？

2.1 UVC规划定义了那些属性：定义在uvc_ctrl.c里面的数组


static struct uvc_control_info uvc_ctrls[] = {{.entity		= UVC_GUID_UVC_PROCESSING, //属于哪一个entity .selector	= UVC_PU_BRIGHTNESS_CONTROL,//用于亮度.index		= 0,// 对应Processing Unit Descriptor 的bmControls[0].size		= 2,//数据长度2个字节.flags		= UVC_CTRL_FLAG_SET_CUR| UVC_CTRL_FLAG_GET_RANGE| UVC_CTRL_FLAG_RESTORE,},
}

2.2 设备支持哪些属性呢

这需要具体去看设备描述符，比如 Processing Unit Descriptor 的bmControls值为7f 14
可知BIT0 为1 表示支持BRIGHTNESS

在代码中

uvc_ctrl_init_device(dev)

对于每一个entity(IT,PU,SU,OT等)

list_for_each_entry(entity, &dev->entities, list)

分别提取对应的控制集（bmControls）以及控制的大小（bControlSize）

if (UVC_ENTITY_TYPE(entity) == UVC_VC_EXTENSION_UNIT) {bmControls = entity->extension.bmControls;bControlSize = entity->extension.bControlSize;} else if (UVC_ENTITY_TYPE(entity) == UVC_VC_PROCESSING_UNIT) {bmControls = entity->processing.bmControls;bControlSize = entity->processing.bControlSize;

计算bmControls 里面1 的个数也就是支持的属性个数

		ncontrols = memweight(bmControls, bControlSize);

为每一个属性分配一个struct uvc_control

entity->controls = kcalloc(ncontrols, sizeof(*ctrl),GFP_KERNEL);

设置这些struct uvc_control

ctrl = entity->controls;for (i = 0; i < bControlSize * 8; ++i) {if (uvc_test_bit(bmControls, i) == 0)continue;ctrl->entity = entity;ctrl->index = i;uvc_ctrl_init_ctrl(dev, ctrl);ctrl++;}

2.3 怎么去操控这些属性呢

参考

uvc_ioctl_queryctrl
---->uvc_query_v4l2_ctrl(chain, qc);
------>uvc_find_control

关于结构体 uvc_control_mapping 用来更加细致的描述属性


struct uvc_control_mapping {struct list_head list;struct list_head ev_subs;__u32 id; __u8 name[32];__u8 entity[16];__u8 selector;__u8 size;__u8 offset;enum v4l2_ctrl_type v4l2_type;__u32 data_type;struct uvc_menu_info *menu_info;__u32 menu_count;__u32 master_id;__s32 master_manual;__u32 slave_ids[2];__s32 (*get) (struct uvc_control_mapping *mapping, __u8 query,const __u8 *data);void (*set) (struct uvc_control_mapping *mapping, __s32 value,__u8 *data);
};

例如

{.id		= V4L2_CID_BRIGHTNESS,  // APP根据ID来找到对应的属性.name		= "Brightness",.entity		= UVC_GUID_UVC_PROCESSING,  // 属于哪了个entity(比如PU).selector	= PU_BRIGHTNESS_CONTROL,    // 用于亮度.size		= 16,                       // 数据占多少位.offset		= 0,                        // 从哪位开始.v4l2_type	= V4L2_CTRL_TYPE_INTEGER,   // 属性类别.data_type	= UVC_CTRL_DATA_TYPE_SIGNED,// 数据类型},