Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   1) .. SPDX-License-Identifier: GPL-2.0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   2) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   3) The Linux USB Video Class (UVC) driver
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   4) ======================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   5) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   6) This file documents some driver-specific aspects of the UVC driver, such as
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   7) driver-specific ioctls and implementation notes.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   8) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   9) Questions and remarks can be sent to the Linux UVC development mailing list at
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  10) linux-uvc-devel@lists.berlios.de.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  11) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  12) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  13) Extension Unit (XU) support
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  14) ---------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  15) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  16) Introduction
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  17) ~~~~~~~~~~~~
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  18) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  19) The UVC specification allows for vendor-specific extensions through extension
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  20) units (XUs). The Linux UVC driver supports extension unit controls (XU controls)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  21) through two separate mechanisms:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  22) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  23)   - through mappings of XU controls to V4L2 controls
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  24)   - through a driver-specific ioctl interface
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  25) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  26) The first one allows generic V4L2 applications to use XU controls by mapping
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  27) certain XU controls onto V4L2 controls, which then show up during ordinary
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  28) control enumeration.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  29) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  30) The second mechanism requires uvcvideo-specific knowledge for the application to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  31) access XU controls but exposes the entire UVC XU concept to user space for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  32) maximum flexibility.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  33) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  34) Both mechanisms complement each other and are described in more detail below.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  35) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  36) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  37) Control mappings
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  38) ~~~~~~~~~~~~~~~~
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  39) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  40) The UVC driver provides an API for user space applications to define so-called
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  41) control mappings at runtime. These allow for individual XU controls or byte
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  42) ranges thereof to be mapped to new V4L2 controls. Such controls appear and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  43) function exactly like normal V4L2 controls (i.e. the stock controls, such as
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  44) brightness, contrast, etc.). However, reading or writing of such a V4L2 controls
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  45) triggers a read or write of the associated XU control.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  46) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  47) The ioctl used to create these control mappings is called UVCIOC_CTRL_MAP.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  48) Previous driver versions (before 0.2.0) required another ioctl to be used
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  49) beforehand (UVCIOC_CTRL_ADD) to pass XU control information to the UVC driver.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  50) This is no longer necessary as newer uvcvideo versions query the information
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  51) directly from the device.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  52) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  53) For details on the UVCIOC_CTRL_MAP ioctl please refer to the section titled
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  54) "IOCTL reference" below.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  55) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  56) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  57) 3. Driver specific XU control interface
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  58) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  59) For applications that need to access XU controls directly, e.g. for testing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  60) purposes, firmware upload, or accessing binary controls, a second mechanism to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  61) access XU controls is provided in the form of a driver-specific ioctl, namely
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  62) UVCIOC_CTRL_QUERY.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  63) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  64) A call to this ioctl allows applications to send queries to the UVC driver that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  65) directly map to the low-level UVC control requests.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  66) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  67) In order to make such a request the UVC unit ID of the control's extension unit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  68) and the control selector need to be known. This information either needs to be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  69) hardcoded in the application or queried using other ways such as by parsing the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  70) UVC descriptor or, if available, using the media controller API to enumerate a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  71) device's entities.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  72) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  73) Unless the control size is already known it is necessary to first make a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  74) UVC_GET_LEN requests in order to be able to allocate a sufficiently large buffer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  75) and set the buffer size to the correct value. Similarly, to find out whether
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  76) UVC_GET_CUR or UVC_SET_CUR are valid requests for a given control, a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  77) UVC_GET_INFO request should be made. The bits 0 (GET supported) and 1 (SET
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  78) supported) of the resulting byte indicate which requests are valid.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  79) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  80) With the addition of the UVCIOC_CTRL_QUERY ioctl the UVCIOC_CTRL_GET and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  81) UVCIOC_CTRL_SET ioctls have become obsolete since their functionality is a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  82) subset of the former ioctl. For the time being they are still supported but
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  83) application developers are encouraged to use UVCIOC_CTRL_QUERY instead.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  84) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  85) For details on the UVCIOC_CTRL_QUERY ioctl please refer to the section titled
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  86) "IOCTL reference" below.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  87) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  88) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  89) Security
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  90) ~~~~~~~~
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  91) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  92) The API doesn't currently provide a fine-grained access control facility. The
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  93) UVCIOC_CTRL_ADD and UVCIOC_CTRL_MAP ioctls require super user permissions.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  94) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  95) Suggestions on how to improve this are welcome.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  96) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  97) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  98) Debugging
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  99) ~~~~~~~~~
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) In order to debug problems related to XU controls or controls in general it is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) recommended to enable the UVC_TRACE_CONTROL bit in the module parameter 'trace'.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) This causes extra output to be written into the system log.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) IOCTL reference
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) ~~~~~~~~~~~~~~~
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) UVCIOC_CTRL_MAP - Map a UVC control to a V4L2 control
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) Argument: struct uvc_xu_control_mapping
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) **Description**:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) 	This ioctl creates a mapping between a UVC control or part of a UVC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117) 	control and a V4L2 control. Once mappings are defined, userspace
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) 	applications can access vendor-defined UVC control through the V4L2
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119) 	control API.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121) 	To create a mapping, applications fill the uvc_xu_control_mapping
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122) 	structure with information about an existing UVC control defined with
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) 	UVCIOC_CTRL_ADD and a new V4L2 control.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125) 	A UVC control can be mapped to several V4L2 controls. For instance,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) 	a UVC pan/tilt control could be mapped to separate pan and tilt V4L2
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127) 	controls. The UVC control is divided into non overlapping fields using
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) 	the 'size' and 'offset' fields and are then independently mapped to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) 	V4L2 control.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131) 	For signed integer V4L2 controls the data_type field should be set to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) 	UVC_CTRL_DATA_TYPE_SIGNED. Other values are currently ignored.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134) **Return value**:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) 	On success 0 is returned. On error -1 is returned and errno is set
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137) 	appropriately.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) 	ENOMEM
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140) 		Not enough memory to perform the operation.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) 	EPERM
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) 		Insufficient privileges (super user privileges are required).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143) 	EINVAL
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144) 		No such UVC control.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145) 	EOVERFLOW
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146) 		The requested offset and size would overflow the UVC control.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) 	EEXIST
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148) 		Mapping already exists.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 150) **Data types**:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 151) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 152) .. code-block:: none
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 153) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 154) 	* struct uvc_xu_control_mapping
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 155) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 156) 	__u32	id		V4L2 control identifier
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 157) 	__u8	name[32]	V4L2 control name
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 158) 	__u8	entity[16]	UVC extension unit GUID
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 159) 	__u8	selector	UVC control selector
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 160) 	__u8	size		V4L2 control size (in bits)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 161) 	__u8	offset		V4L2 control offset (in bits)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 162) 	enum v4l2_ctrl_type
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 163) 		v4l2_type	V4L2 control type
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 164) 	enum uvc_control_data_type
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 165) 		data_type	UVC control data type
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 166) 	struct uvc_menu_info
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 167) 		*menu_info	Array of menu entries (for menu controls only)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 168) 	__u32	menu_count	Number of menu entries (for menu controls only)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 169) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 170) 	* struct uvc_menu_info
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 171) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 172) 	__u32	value		Menu entry value used by the device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 173) 	__u8	name[32]	Menu entry name
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 174) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 175) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 176) 	* enum uvc_control_data_type
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 177) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 178) 	UVC_CTRL_DATA_TYPE_RAW		Raw control (byte array)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 179) 	UVC_CTRL_DATA_TYPE_SIGNED	Signed integer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 180) 	UVC_CTRL_DATA_TYPE_UNSIGNED	Unsigned integer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 181) 	UVC_CTRL_DATA_TYPE_BOOLEAN	Boolean
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 182) 	UVC_CTRL_DATA_TYPE_ENUM		Enumeration
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 183) 	UVC_CTRL_DATA_TYPE_BITMASK	Bitmask
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 184) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 185) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 186) UVCIOC_CTRL_QUERY - Query a UVC XU control
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 187) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 188) Argument: struct uvc_xu_control_query
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 189) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 190) **Description**:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 191) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 192) 	This ioctl queries a UVC XU control identified by its extension unit ID
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 193) 	and control selector.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 194) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 195) 	There are a number of different queries available that closely
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 196) 	correspond to the low-level control requests described in the UVC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 197) 	specification. These requests are:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 198) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 199) 	UVC_GET_CUR
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 200) 		Obtain the current value of the control.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 201) 	UVC_GET_MIN
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 202) 		Obtain the minimum value of the control.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 203) 	UVC_GET_MAX
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 204) 		Obtain the maximum value of the control.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 205) 	UVC_GET_DEF
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 206) 		Obtain the default value of the control.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 207) 	UVC_GET_RES
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 208) 		Query the resolution of the control, i.e. the step size of the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 209) 		allowed control values.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 210) 	UVC_GET_LEN
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 211) 		Query the size of the control in bytes.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 212) 	UVC_GET_INFO
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 213) 		Query the control information bitmap, which indicates whether
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 214) 		get/set requests are supported.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 215) 	UVC_SET_CUR
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 216) 		Update the value of the control.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 217) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 218) 	Applications must set the 'size' field to the correct length for the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 219) 	control. Exceptions are the UVC_GET_LEN and UVC_GET_INFO queries, for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 220) 	which the size must be set to 2 and 1, respectively. The 'data' field
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 221) 	must point to a valid writable buffer big enough to hold the indicated
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 222) 	number of data bytes.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 223) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 224) 	Data is copied directly from the device without any driver-side
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 225) 	processing. Applications are responsible for data buffer formatting,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 226) 	including little-endian/big-endian conversion. This is particularly
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 227) 	important for the result of the UVC_GET_LEN requests, which is always
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 228) 	returned as a little-endian 16-bit integer by the device.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 229) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 230) **Return value**:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 231) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 232) 	On success 0 is returned. On error -1 is returned and errno is set
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 233) 	appropriately.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 234) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 235) 	ENOENT
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 236) 		The device does not support the given control or the specified
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 237) 		extension unit could not be found.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 238) 	ENOBUFS
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 239) 		The specified buffer size is incorrect (too big or too small).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 240) 	EINVAL
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 241) 		An invalid request code was passed.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 242) 	EBADRQC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 243) 		The given request is not supported by the given control.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 244) 	EFAULT
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 245) 		The data pointer references an inaccessible memory area.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 246) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 247) **Data types**:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 248) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 249) .. code-block:: none
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 250) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 251) 	* struct uvc_xu_control_query
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 252) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 253) 	__u8	unit		Extension unit ID
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 254) 	__u8	selector	Control selector
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 255) 	__u8	query		Request code to send to the device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 256) 	__u16	size		Control data size (in bytes)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 257) 	__u8	*data		Control value