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。
- 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,
}
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：
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)
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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