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Improve the uhid(4) manual:
* Include the relevant header in the synopsis
* Document all supported ioctl commands
* Emphasis that a pointer is required to all ioctl commands
* Make the write(2) semantics a bit clearer
* Add files section
* Document errors

ok jmc@

.\" $OpenBSD: uhid.4,v 1.20 2021/09/15 04:59:26 anton Exp $
.\" $NetBSD: uhid.4,v 1.13 2001/12/29 14:41:59 augustss Exp $
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.\" by Lennart Augustsson.
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.Dd $Mdocdate: September 15 2021 $
.Dt UHID 4
.Os
.Sh NAME
.Nm uhid
.Nd USB generic HID support
.Sh SYNOPSIS
.Cd "uhid* at uhidev?"
.Pp
.In dev/usb/usb.h
.Sh DESCRIPTION
The
.Nm
driver provides support for all HID (Human Interface Device) interfaces
in USB devices that do not have a special driver.
.Pp
The device handles the following
.Xr ioctl 2
calls:
.Bl -tag -width indent
.It Dv USB_GET_DEVICEINFO Fa struct usb_device_info *devinfo
Get summarized information about the device.
.It Dv USB_GET_REPORT_ID Fa int *repid
Get the report identifier used by this HID report.
.It Dv USB_GET_REPORT_DESC Fa struct usb_ctl_report_desc *repdesc
Get the HID report descriptor.
Using this descriptor the exact layout and meaning of data to/from
the device can be found.
The report descriptor is delivered without any processing.
.Bd -literal
struct usb_ctl_report_desc {
    int     ucrd_size;
    u_char  ucrd_data[1024];	/* filled data size will vary */
};
.Ed
.It Dv USB_GET_REPORT Fa struct usb_ctl_report *rep
Get a report from the device without waiting for data on
the interrupt pipe.
The
.Fa ucr_report
field indicates which report is requested.
It should be
.Dv UHID_INPUT_REPORT ,
.Dv UHID_OUTPUT_REPORT ,
or
.Dv UHID_FEATURE_REPORT .
.Bd -literal
struct usb_ctl_report {
	int	ucr_report;
	u_char	ucr_data[1024];	/* filled data size will vary */
};
.Ed
.It Dv USB_SET_REPORT Fa struct usb_ctl_report *rep
Set a report in the device.
The
.Dv report
field indicates which report is to be set.
It should be
.Dv UHID_INPUT_REPORT ,
.Dv UHID_OUTPUT_REPORT ,
or
.Dv UHID_FEATURE_REPORT .
.El
.Pp
The generic ioctls
.Dv FIONBIO
and
.Dv FIOASYNC
are supported by
.Nm .
.Pp
Use
.Xr read 2
to get data from the device.
Data should be read in chunks of the size prescribed by the report descriptor.
.Pp
Use
.Xr write 2
to send data to the device.
Equivalent to issuing an
.Xr ioctl 2
.Dv USB_SET_REPORT
request with the report set to
.Dv UHID_OUTPUT_REPORT .
Data should be written in chunks of the size prescribed by the report
descriptor.
.Sh FILES
.Bl -tag -width /dev/tun* -compact
.It Pa /dev/uhid*
.El
.Sh ERRORS
If
.Xr ioctl 2
fails,
.Xr errno 2
is set to one of the following:
.Bl -tag -width Er
.It Bq Er EIO
The device could not fulfill a
.Dv USB_GET_REPORT
or
.Dv USB_SET_REPORT
request.
.It Bq Er EINVAL
The report specified by the
.Fa ucr_report
field in a
.Dv USB_GET_REPORT
or
.Dv USB_SET_REPORT
request was invalid.
.It Bq Er ENOTTY
Unrecognized command.
.El
.Pp
If
.Xr read 2
fails,
.Xr errno 2
is set to one of the following:
.Bl -tag -width Er
.It Bq Er EIO
The device has already been detached.
.It Bq Er EWOULDBLOCK
Non-blocking I/O was selected and no data were available.
.El
.Pp
If
.Xr write 2
fails,
.Xr errno 2
is set to one of the following:
.Bl -tag -width Er
.It Bq Er EIO
The device has already been detached or the same device does not have a
corresponding output report.
.It Bq Er EMSGSIZE
The size of the supplied data exceeds the size of the output report.
.El
.Sh SEE ALSO
.Xr usbhidctl 1 ,
.Xr usbhid 3 ,
.Xr intro 4 ,
.Xr uhidev 4 ,
.Xr usb 4
.Sh HISTORY
The
.Nm
driver
appeared in
.Ox 2.6 .