Documentation/hid/uhid.rst

2 UHID - User-space I/O driver support for HID subsystem
5 UHID allows user-space to implement HID transport drivers. Please see
6 hid-transport.rst for an introduction into HID transport drivers. This document
9 With UHID, a user-space transport driver can create kernel hid-devices for each
10 device connected to the user-space controlled bus. The UHID API defines the I/O
11 events provided from the kernel to user-space and vice versa.
13 There is an example user-space application in ./samples/uhid/uhid-example.c
16 ------------
18 UHID is accessed through a character misc-device. The minor number is allocated
25 write()'ing "struct uhid_event" objects. Non-blocking operations are supported
45 payload-structure available in the union "u" (except for empty payloads). This
56 reference-counting in user-space. That is, you will never receive multiple
58 ref-counting for you.
59 You may decide to ignore UHID_OPEN/UHID_CLOSE, though. I/O is allowed even
71 The kernel blocks internal driver-execution during such round-trips (times out
72 after a hard-coded period).
81 -------
84 not supported, it will return -EOPNOTSUPP. If the payload is invalid, then
85 -EINVAL is returned, otherwise, the amount of data that was read is returned and
87 writes are always handled immediately in a non-blocking fashion. Future requests
104   contains a data-payload. This is the raw data that you read from your device
120 ------
132       - UHID_DEV_NUMBERED_FEATURE_REPORTS
133       - UHID_DEV_NUMBERED_OUTPUT_REPORTS
134       - UHID_DEV_NUMBERED_INPUT_REPORTS
136           Each of these flags defines whether a given report-type uses numbered
137           reports. If numbered reports are used for a type, all messages from
138           the kernel already have the report-number as prefix. Otherwise, no
140           For messages sent by user-space to the kernel, you must adjust the
157   it is useful for power-management. As long as you haven't received this event
169   This may be received even though you haven't received UHID_OPEN yet.
173   on the control channel as described in the HID specs. The report-type and
174   report-number are available in the payload.
183   never re-used, so conflicts cannot happen.
191 ----------------------------------------------------