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7 Questions and remarks can be sent to the Linux UVC development mailing list at
20   - through mappings of XU controls to V4L2 controls
23 The first one allows generic V4L2 applications to use XU controls by mapping
27 The second mechanism requires uvcvideo-specific knowledge for the application to
28 access XU controls but exposes the entire UVC XU concept to user space for
36 The UVC driver provides an API for user space applications to define so-called
38 ranges thereof to be mapped to new V4L2 controls. Such controls appear and
43 The ioctl used to create these control mappings is called UVCIOC_CTRL_MAP.
44 Previous driver versions (before 0.2.0) required another ioctl to be used
45 beforehand (UVCIOC_CTRL_ADD) to pass XU control information to the UVC driver.
49 For details on the UVCIOC_CTRL_MAP ioctl please refer to the section titled
55 For applications that need to access XU controls directly, e.g. for testing
56 purposes, firmware upload, or accessing binary controls, a second mechanism to
60 A call to this ioctl allows applications to send queries to the UVC driver that
61 directly map to the low-level UVC control requests.
63 In order to make such a request the UVC unit ID of the control's extension unit
64 and the control selector need to be known. This information either needs to be
66 UVC descriptor or, if available, using the media controller API to enumerate a
69 Unless the control size is already known it is necessary to first make a
70 UVC_GET_LEN requests in order to be able to allocate a sufficiently large buffer
71 and set the buffer size to the correct value. Similarly, to find out whether
79 application developers are encouraged to use UVCIOC_CTRL_QUERY instead.
81 For details on the UVCIOC_CTRL_QUERY ioctl please refer to the section titled
90 Suggestions on how to improve this are welcome.
95 In order to debug problems related to XU controls or controls in general it is
96 recommended to enable the UVC_TRACE_CONTROL bit in the module parameter 'trace'.
97 This causes extra output to be written into the system log.
102 ---- UVCIOC_CTRL_MAP - Map a UVC control to a V4L2 control ----
116 	A UVC control can be mapped to several V4L2 controls. For instance,
117 	a UVC pan/tilt control could be mapped to separate pan and tilt V4L2
119 	the 'size' and 'offset' fields and are then independently mapped to
122 	For signed integer V4L2 controls the data_type field should be set to
130 		Not enough memory to perform the operation.
182 	correspond to the low-level control requests described in the UVC
204 	Applications must set the 'size' field to the correct length for the
206 	which the size must be set to 2 and 1, respectively. The 'data' field
207 	must point to a valid writable buffer big enough to hold the indicated
237 	__u8	query		Request code to send to the device