media/drivers/uvcvideo.rst

1 .. SPDX-License-Identifier: GPL-2.0
6 This file documents some driver-specific aspects of the UVC driver, such as
7 driver-specific ioctls and implementation notes.
10 linux-media@vger.kernel.org.
13 Extension Unit (XU) support
14 ---------------------------
19 The UVC specification allows for vendor-specific extensions through extension
20 units (XUs). The Linux UVC driver supports extension unit controls (XU controls)
23   - through mappings of XU controls to V4L2 controls
24   - through a driver-specific ioctl interface
30 The second mechanism requires uvcvideo-specific knowledge for the application to
40 The UVC driver provides an API for user space applications to define so-called
61 access XU controls is provided in the form of a driver-specific ioctl, namely
65 directly map to the low-level UVC control requests.
67 In order to make such a request the UVC unit ID of the control's extension unit
92 The API doesn't currently provide a fine-grained access control facility. The
109 UVCIOC_CTRL_MAP - Map a UVC control to a V4L2 control
118 	applications can access vendor-defined UVC control through the V4L2
136 	On success 0 is returned. On error -1 is returned and errno is set
152 .. code-block:: none
158 	__u8	entity[16]	UVC extension unit GUID
186 UVCIOC_CTRL_QUERY - Query a UVC XU control
192 	This ioctl queries a UVC XU control identified by its extension unit ID
196 	correspond to the low-level control requests described in the UVC
224 	Data is copied directly from the device without any driver-side
226 	including little-endian/big-endian conversion. This is particularly
228 	returned as a little-endian 16-bit integer by the device.
232 	On success 0 is returned. On error -1 is returned and errno is set
237 		extension unit could not be found.
249 .. code-block:: none
253 	__u8	unit		Extension unit ID