A driver for the NXP SC16IS7xx family of UART chips. This family is
mostly a 16C450 with features from the 16C550, 16C650 and 16C750 and
makes use of src/sys/dev/ic/com.c for much of the heavy lifting.

A BIG difference is that the chip family is attached via a I2C or SPI
bus and is in no way, shape or form, attached to the computer via a
computer bus.

Since spin locks are not allowed to be held while calling to the I2C
or SPI framework com.c grew a new hw feature flag where it could be
run at something other than a hard IP level and doesn't hold spin lock
(for very long). In particular, IPL_SOFTSERIAL. This method is
enabled via a hw feature flag and should not effect any other use of
com.c. Other changes with this new method of use include the use of
workqueues and such.

A further feature added to com.c was the abilty to take advantage of
the MCR prescaler that is present in the SC16IS7xx family and likely
present in the 16C650. This prescaler is tried if the baud rate
requested can not be met with the frequency oscillator that the chip is
built with.

The chip family does not use any particular frequency oscillator for
the baud rate generator. In order to deal with this the frequency can
be set via sysctl, a kernel option or with a FDT overlay if that is
supported.

Most of the features of the chip family are supported including the
gpio pins via gpiobus(4) that are present with some of the family
members.

The chip can attach via I2C or SPI and can make sure of FDT if that is
present in the system.

This chip family has been around for quite some time and there are a
number of breakout boards on Amazon. It is also reasonably priced and
you can roll your own board if you can perform simple SMD soldering as
very few additional components are required.

Mention emcfan(4) and emcfanctl(8)

Mention ds28e17iic(4)

Mention umcpmio(4)

Mention ds2482ow

branches: 1.35.4;


Mention the driver for the Bosch BMP280/BME280

Mention the AHT20 driver

Mention the SCMD device

s/covert/convert/ in comment.

Mention sht3xtemp(4)

Add sgp40mox(4)

Add sht4xtemp(4). Sort.

sort

iic.4: add missing client devs (those with man pages, many don't have one)

Remove dead references

iic.4: Add FILES section. Fix copypasto.

Describe the i2c ioctl interface

iic.4: add ssdfb

branches: 1.22.6;
Fix comment.

Finally, remove extraneous entries for macppc's "iic at cuda". We
don't need three entries that differ only in wildcarding.

Ooopppsss! Put the .Sh DESCRIPTION where it belongs, _after_ the
list of config attachments.

Hmmm, for some reason the first entry in the generated list is not
in collating-sequence order. Move it to the proper place in the
list.

Bump date for previous two changes.

Fix the commands-to-generate-the-attachment list to use tab's instead
of multiple spaces in the regex bracket expressions, and alert the
reader to this. Otherwise, a cut-and-paste might simply expand the
tab characters to some number of spaces, and the result won't find
what you're looking for!

XXX Despite the indication that these commands should be run in csh
(or derivative), they seem to run just fine under /bin/sh as well.

Regen attachment list, since we just added "iic* at imcsmb?"

This regen also caught a few other missing entries.

Remove Tn.

Remove port-acorn26

OK core@

Update supported masters and slaves.

branches: 1.12.8;
Merge riastradh-drm2 to HEAD.

Use Mt for email addresses.

branches: 1.10.2; 1.10.8; 1.10.12;
Xref i2cscan(8).

Install dev/i2c/i2c_io.h and implement the API in the iic(4) driver.
Obsolete the I2C_SCAN option as this can now be done from userland.

Also mention gpioiic(4).

Sort SEE ALSO.

Xref dtviic(4).

Note options I2C_SCAN.

Add man page and cross-refs for experimental acpismbus(4)

Kill empty lines.

Drop trailing whitespace. Add a missing continuation line. Use more .An.

Add iic(4) manpage, partly taken from OpenBSD.