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Dynamic controls API -------------------- This file documents the dynamic controls API and its associated ioctls. Please keep in mind that this is a work in progress. The API can change at any time, and the documentation is probably unaccurate. Questions and remarks can be sent to the Linux UVC development mailing list at linux-uvc-devel@lists.berlios.de. 1. Introduction The UVC specification allows for vendor-specific extensions through extension units. With more and more products being UVC compliant, the number of controls defined through extension units is expected to grow rapidly. The Linux UVC driver supports extension unit controls (XU controls) through a hardcode control list. This implementation requires vendors to submit a list of their controls to the Linux UVC project, and wastes kernel memory to store control information that are useful for a small number of cameras only. The dynamic controls API aims at solving those issues. The basic idea is to provide a userspace API through which applications can add control definitions at runtime. 2. Security The API doesn't currently provide any access control facility. Any application allowed to access a UVC device will be able to add control definitions with no limit. Suggestions are welcome. 3. IOCTLs ---- UVCIOC_CTRL_ADD - Define a vendor UVC control ---- Argument: struct uvc_xu_control_info Description: This ioctl allows userspace applications to add an Extension Unit UVC control definition to the driver. Return value: On success 0 is returned. On error -1 is returned and errno is set appropriately. ENOMEM Not enough memory to perform the operation. EEXIST Control is already defined. Data types: * struct uvc_xu_control_info __u8 entity[16] Extension unit GUID __u8 index Control index in the unit's bmControl bit field __u8 selector Control selector __u16 size Control size (in bytes) __u32 flags See below * struct uvc_xu_control_info flags field UVC_CONTROL_SET_CUR Control is writable. UVC_CONTROL_GET_CUR Control is readable. UVC_CONTROL_GET_MIN Control supports GET MIN queries. UVC_CONTROL_GET_MAX Control supports GET MAX queries. UVC_CONTROL_GET_RES Control supports GET RES queries. UVC_CONTROL_GET_DEF Control supports GET DEF queries. UVC_CONTROL_RESTORE Control should be restored when resuming from sleep. ---- UVCIOC_CTRL_MAP - Map a UVC control to a V4L2 control ---- Argument: struct uvc_xu_control_mapping Description: This ioctl creates a mapping between a UVC control or part of a UVC control and a V4L2 control. Once mappings are defined, userspace applications can access vendor-defined UVC control through the V4L2 control API. To create a mapping, applications fill the uvc_xu_control_mapping structure with information about an existing UVC control defined with UVCIOC_CTRL_ADD and a new V4L2 control. A UVC control can be mapped to several V4L2 controls. For instance, a UVC pan/tilt control could be mapped to separate pan and tilt V4L2 controls. The UVC control is divided into non overlapping fields using the 'size' and 'offset' fields and are then independantly mapped to V4L2 control. For signed integer V4L2 controls the data_type field should be set to UVC_CTRL_DATA_TYPE_SIGNED. Other values are currently ignored. Return value: On success 0 is returned. On error -1 is returned and errno is set appropriately. ENOMEM Not enough memory to perform the operation. EINVAL No such UVC control. EOVERFLOW The requested offset and size would overflow the UVC control. EEXIST Mapping already exists. Data types: * struct uvc_xu_control_mapping __u32 id V4L2 control identifier __u8 name[32] V4L2 control name __u8 entity[16] UVC extension unit GUID __u8 selector UVC control selector __u8 size V4L2 control size (in bits) __u8 offset V4L2 control offset (in bits) enum v4l2_ctrl_type v4l2_type V4L2 control type enum uvc_control_data_type data_type UVC control data type * enum uvc_control_data_type UVC_CTRL_DATA_TYPE_RAW Raw control (byte array) UVC_CTRL_DATA_TYPE_SIGNED Signed integer UVC_CTRL_DATA_TYPE_UNSIGNED Unsigned integer UVC_CTRL_DATA_TYPE_BOOLEAN Boolean UVC_CTRL_DATA_TYPE_ENUM Enumeration UVC_CTRL_DATA_TYPE_BITMASK Bitmask ---- UVCIOC_CTRL_GET - Get the value of a UVC control ---- Argument: struct uvc_xu_control Description: This ioctl retrieves the current value of the UVC control identified by its extension unit ID and control selector. Applications must set the control size and provide a pointer to a writable buffer big enough to fit the data. Data are taken directly from the device without any driver-side processing. Applications are responsible for data buffer formatting, including little-endian/big-endian conversion. Return value: On success 0 is returned. On error -1 is returned and errno is set appropriately. EINVAL No such UVC control, or control isn't readable. EFAULT data references an inaccessible memory area. Data types: * struct uvc_xu_control __u8 unit Extension unit ID __u8 selector Control selector __u16 size Control data size (in bytes) __u8 *data Control value ---- UVCIOC_CTRL_SET - Set the value of a UVC control ---- Argument: struct uvc_xu_control Description: This ioctl sets the value of the UVC control identified by its extension unit ID and control selector. Applications must set the control size and provide a pointer to a readable buffer containing the data. Data are passed directly to the device without any driver-side processing. Applications are responsible for data buffer formatting, including little-endian/big-endian conversion. Return value: On success 0 is returned. On error -1 is returned and errno is set appropriately. EINVAL No such UVC control, or control isn't writable. EFAULT data references an inaccessible memory area. Data types: * struct uvc_xu_control See UVCIOC_CTRL_GET