2 files changed, 135 insertions, 0 deletions

diff --git a/share/man/man4/Makefile b/share/man/man4/Makefile
index abdc1b0f4c4b..fa2af9d32aea 100644
--- a/share/man/man4/Makefile
+++ b/share/man/man4/Makefile
@@ -197,6 +197,7 @@ MAN=	aac.4 \
 	${_hptnr.4} \
 	${_hptrr.4} \
 	hsctrl.4 \
+	htu21.4 \
 	${_hv_kvp.4} \
 	${_hv_netvsc.4} \
 	${_hv_storvsc.4} \
diff --git a/share/man/man4/htu21.4 b/share/man/man4/htu21.4
new file mode 100644
index 000000000000..990852027e09
--- /dev/null
+++ b/share/man/man4/htu21.4
@@ -0,0 +1,134 @@
+.\"
+.\" SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+.\"
+.\" Copyright (c) 2021 Andriy Gapon <avg@FreeBSD.org>
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd January 19, 2021
+.Dt HTU21 4
+.Os
+.Sh NAME
+.Nm htu21
+.Nd driver for HTU21D and compatible temperature and humidity sensors
+.Sh SYNOPSIS
+To compile this driver into the kernel,
+place the following lines in your
+kernel configuration file:
+.Bd -ragged -offset indent
+.Cd "device htu21"
+.Cd "device iicbus"
+.Ed
+.Pp
+Alternatively, to load the driver as a
+module at boot time, place the following line in
+.Xr loader.conf 5 :
+.Bd -literal -offset indent
+htu21_load="YES"
+.Ed
+.Sh DESCRIPTION
+The
+.Nm
+driver provides temperature and relative humidity readings over I2C bus
+for the supported sensors:
+.Bl -bullet -compact
+.It
+HTU21D
+.It
+SHT21
+.It
+Si7021
+.El
+.Pp
+The
+.Nm
+driver reports data via
+.Xr sysctl 8
+entries in the device's node in the
+.Xr sysctl 8
+tree:
+.Bl -tag -width temperature
+.It temperature
+The temperature, in hundredths of Kelvin.
+.It humidity
+The relative humidity, in hundredths of a percent.
+.It crc_errors
+The number of CRC errors in reading the measurements from the device.
+.It power
+The good power indication.
+This can be useful with battery powered sensors.
+.It heater
+The built-in heater control.
+The heater can be used for testing and for recovery from saturation
+after high humidity.
+.It hold_bus
+Whether the sensor should hold SCL low while performing the measurement.
+Normally, the sensor releases the bus and NACKs all accessed until the
+measurement is completed.
+The hold mode may be useful in mult-master environments.
+.El
+.Pp
+On an
+.Xr FDT 4
+based system the following properties must be set:
+.Bl -tag -width "compatible"
+.It Va compatible
+Must be set to "meas,htu21".
+.It Va reg
+The I2C address of
+.Nm .
+Although, it is hard-wired to 0x40 (7-bit) on all supported sensors.
+.El
+.Pp
+The DTS part for a
+.Nm
+device usually looks like:
+.Bd -literal
+/ {
+
+	...
+	htu21d {
+		compatible = "meas,htu21";
+		reg = <0x40>;
+	};
+};
+.Ed
+.Sh SEE ALSO
+.Xr fdt 4 ,
+.Xr iicbus 4 ,
+.Xr sysctl 8
+.Sh HISTORY
+The
+.Nm
+driver and this manual page was written by
+.An Andriy Gapon Aq Mt avg@FreeBSD.org .
+.Sh BUGS
+There is no way to control the measurment resolution.
+.Pp
+Some sensor variants do not provide a serial number or use an incompatible
+format.
+The
+.Nm
+driver does not distinguish those variants and may complain about incorrect
+serial number checksum.