本文主要是介绍UVC系列4-定制Android kernel UVC部分支持相对和绝对参数，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
1、添加参数
在熟悉了android uvc控制参数和UVC协议之后，现在可以着手定制android UVC协议了，添加相对控制参数。
1.1 添加相对控制pan和tilt
第一步，添加相对控制pan和tilt修改的文件是：drivers\media\usb\uvc\uvc_ctrl.c
在uvc_control_info uvc_ctrls[]结构体中添加：
{.entity = UVC_GUID_UVC_CAMERA,.selector = UVC_CT_PANTILT_RELATIVE_CONTROL,.index = 12,.size = 4,.flags = UVC_CTRL_FLAG_SET_CUR|UVC_CTRL_FLAG_GET_RANGE|UVC_CTRL_FLAG_AUTO_UPDATE,
}
在结构体uvc_control_mapping uvc_ctrl_mappings[]中添加：
{.id = V4L2_CID_PAN_RELATIVE,.name = "Pan (Relative)",.entity = UVC_GUID_UVC_CAMERA,.selector = UVC_CT_PANTILT_RELATIVE_CONTROL,.size = 16,.offset = 0,.v4l2_type = V4L2_CTRL_TYPE_INTEGER,.data_type = UVC_CTRL_DATA_TYPE_SIGNED,.get = uvc_ctrl_get_rel_speed,.set = uvc_ctrl_set_rel_speed,
},
{.id = V4L2_CID_TILT_RELATIVE,.name= "Tilt (Relative)",.entity= UVC_GUID_UVC_CAMERA,.selector= UVC_CT_PANTILT_RELATIVE_CONTROL,.size= 16,.offset= 16,.v4l2_type= V4L2_CTRL_TYPE_INTEGER,.data_type= UVC_CTRL_DATA_TYPE_SIGNED,.get= uvc_ctrl_get_rel_speed,.set= uvc_ctrl_set_rel_speed,
}
1.2 添加pan和tilt的速度控制
其中uvc_ctrl_get_rel_speed和uvc_ctrl_set_rel_speed映射到的方法对应UVC协议里面的速度控制，在uvc_ctrl.c文件中也要添加这两个方法的实现，与zoom对应的控制方法类似，具体实现方法是：
static __s32 uvc_ctrl_get_rel_speed(structuvc_control_mapping *mapping,__u8query, const __u8 *data)
{intfirst = mapping->offset / 8;__s8rel = (__s8)data[first];switch (query) {case UVC_GET_CUR:return (rel == 0) ? 0 : (rel > 0 ?data[first+1]:-data[first+1]);case UVC_GET_MIN:return -data[first+1];case UVC_GET_MAX:case UVC_GET_RES:case UVC_GET_DEF:default:return data[first+1];
}
}
static void uvc_ctrl_set_rel_speed(structuvc_control_mapping *mapping,__s32 value, __u8 *data)
{intfirst = mapping->offset / 8;data[first] = value == 0 ? 0 : (value > 0)? 1 : 0xff;data[first+1] = min_t(int, abs(value), 0xff);
}
可以看到这里的赋值也是与UVC协议对应的。另外针对绝对控制，目前在结构体uvc_control_mappinguvc_ctrl_mappings[]中的定义是：
{.id = V4L2_CID_PAN_ABSOLUTE,.name = "Pan (Absolute)",.entity = UVC_GUID_UVC_CAMERA,.selector = UVC_CT_PANTILT_ABSOLUTE_CONTROL,.size = 32,.offset = 0,.v4l2_type = V4L2_CTRL_TYPE_INTEGER,.data_type = UVC_CTRL_DATA_TYPE_UNSIGNED,
},
{.id = V4L2_CID_TILT_ABSOLUTE,.name = "Tilt (Absolute)",.entity = UVC_GUID_UVC_CAMERA,.selector = UVC_CT_PANTILT_ABSOLUTE_CONTROL,.size = 32,.offset = 32,.v4l2_type = V4L2_CTRL_TYPE_INTEGER,.data_type = UVC_CTRL_DATA_TYPE_UNSIGNED,
}
可以看看这两个控制参数的data_type是UVC_CTRL_DATA_TYPE_UNSIGNED，而UVC协议里面定义的是：
1.3 修改参数类型
Value的类型是signed number，此时我们需要将UNSIGNED改为signed，将这个data_type统一改成signed，即UVC_CTRL_DATA_TYPE_SIGNED。
下一步uvc_control_mapping uvc_ctrl_mappings[]中添加速度控制的参数，如下：
{.id = V4L2_CID_PAN_SPEED,.name = "Pan (Speed)",.entity = UVC_GUID_UVC_CAMERA,.selector = UVC_CT_PANTILT_RELATIVE_CONTROL,.size = 16,.offset = 0,.v4l2_type = V4L2_CTRL_TYPE_INTEGER,.data_type = UVC_CTRL_DATA_TYPE_SIGNED,.get = uvc_ctrl_get_rel_speed,.set = uvc_ctrl_set_rel_speed,
},
{.id = V4L2_CID_TILT_SPEED,.name = "Tilt (Speed)",.entity = UVC_GUID_UVC_CAMERA,.selector = UVC_CT_PANTILT_RELATIVE_CONTROL,.size =16,.offset = 16,.v4l2_type = V4L2_CTRL_TYPE_INTEGER,.data_type = UVC_CTRL_DATA_TYPE_SIGNED,.get = uvc_ctrl_get_rel_speed,.set = uvc_ctrl_set_rel_speed,
}
针对相对控制的两个参数id V4L2_CID_PAN_RELATIVE和V4L2_CID_PAN_RELATIVE，两个控制速度的参数V4L2_CID_PAN_SPEED和V4L2_CID_TILT_SPEED需要定义，修改两个文件，第一个文件位置位于drivers\media\v4l2-core\v4l2-ctrls.c文件中，const char *v4l2_ctrl_get_name中添加：
caseV4L2_CID_PAN_RELATIVE: return"Pan, Relative";
caseV4L2_CID_TILT_RELATIVE: return"Tilt, Relative";
caseV4L2_CID_PAN_SPEED: return"Pan, Speed";
caseV4L2_CID_TILT_SPEED: return"Tilt, Speed";
第二个文件位于include/uapi/linux/v4l2-controls.h，添加定义：
#define V4L2_CID_PAN_RELATIVE (V4L2_CID_CAMERA_CLASS_BASE+4)
#define V4L2_CID_TILT_RELATIVE (V4L2_CID_CAMERA_CLASS_BASE+5)
#define V4L2_CID_PAN_SPEED (V4L2_CID_CAMERA_CLASS_BASE+32)
#define V4L2_CID_TILT_SPEED (V4L2_CID_CAMERA_CLASS_BASE+33)
1.4 xml文件修改
另外还有两个xml说明文件，需要添加这两个控制的说明，分别是：
Documentation/DocBook/media/v4l/controls.xml
Documentation/DocBook/media/v4l/compat.xml
具体修改网址可以参考：
https://patchwork.kernel.org/patch/4836491/
至此，android UVC kernel部分定制完毕，下一步就是打通app到底层kernel的通道,将这些代码合入完毕之后，开始编译kernel代码，并刷机重启。
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