sys: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

sys: Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

Remove unused uart_devclass.

uart: plug a set-but-not-used var

Sponsored by: Rubicon Communications, LLC ("Netgate")

uart: Remove CTLFLAG_NEEDGIANT from sysctl.

MFC after: 2 weeks

Export a sysctl count of RX FIFO overrun events.

uart(4) backends currently detect RX FIFO overrun errors and report
them to the uart(4) core layer. They are then reported to the generic
TTY layer which promptly ignores them. As a result, there is
currently no good way to determine if a uart is experiencing RX FIFO
overruns. One could add a generic per-tty counter, but there did not
appear to be a good way to export those. Instead, add a sysctl under
the uart(4) sysctl tree to export the count of overruns.

Reviewed by: brooks
MFC after: 2 weeks
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D24368

Mark more nodes as CTLFLAG_MPSAFE or CTLFLAG_NEEDGIANT (17 of many)

r357614 added CTLFLAG_NEEDGIANT to make it easier to find nodes that are
still not MPSAFE (or already are but aren’t properly marked).
Use it in preparation for a general review of all nodes.

This is non-functional change that adds annotations to SYSCTL_NODE and
SYSCTL_PROC nodes using one of the soon-to-be-required flags.

Mark all obvious cases as MPSAFE. All entries that haven't been marked
as MPSAFE before are by default marked as NEEDGIANT

Approved by: kib (mentor, blanket)
Commented by: kib, gallatin, melifaro
Differential Revision: https://reviews.freebsd.org/D23718

Use callout_func_t instead of the deprecated timeout_t.

Reviewed by: kib, imp
Differential Revision: https://reviews.freebsd.org/D22752

add snps IP uart support / genaralize UART

This is an amalgam of a patch by Doug Ambrisko to
generalize uart_acpi_find_device, imp moving the
ACPI table to uart_dev_ns8250.c and advice by jhb
to work around a bug in the EPYC 3151 BIOS
(the BIOS incorrectly marks the serial ports as
disabled)

Reviewed by: imp
MFC after: 8 weeks
Differential Revision: https://reviews.freebsd.org/D16432

sys/dev: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

Allow setting access-width for UART registers.

This is required for FDT's standard "reg-io-width" property
(similar to "reg-shift" property) found in many DTS files.

This fixes operation on Altera Arria 10 SOC Development Kit,
where standard ns8250 uart allows 4-byte access only.

Reviewed by: kan, marcel
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D9785

Allow uart(4) to use MSI interrupts on single-port PCI instances.

Do this here as puc(4) disallows single-port instances; at least
one multi-port PCIe UART chip (in this case, the ASIX MCS9922)
present separate PCI configuration space (functions) for each UART.

Tested using lrzsz and a null-modem cable. The ExpressCard/34
variants containing the MCS9922 should also use MSI with this change.

Reviewed by: jhb, imp, rpokala
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D9123

Do not reallocate driver softc for uart unnecessarily.

Do not assume that all uart drivers use uart_softc structure as is.
Some do a sensible thing and do declare their uart class and driver
properly and arrive into uart_bus_attach with suitably sized softc.

Submitted by: kan
Sponsored by: DARPA, AFRL

Fix UART PPS capture mode printing

* Add breaks to prevent fallthrough and printing of multiple modes.
* Only check the mode, mask out all other bits.

Restore uart PPS signal capture polarity to its historical norm, and add an
option to invert the polarity in software. Also add an option to capture
very narrow pulses by using the hardware's MSR delta-bit capability of
latching line state changes.

This effectively reverts the mistake I made in r286595 which was based on
empirical measurements made on hardware using TTL-level signaling, in which
the logic levels are inverted from RS-232. Thus, this re-syncs the polarity
with the requirements of RFC 2783, which is writen in terms of RS-232
signaling.

Narrow-pulse mode uses the ability of most ns8250 and similar chips to
provide a delta indication in the modem status register. The hardware is
able to notice and latch the change when the pulse width is shorter than
interrupt latency, which results in the signal no longer being asserted by
time the interrupt service code runs. When running in this mode we get
notified only that "a pulse happened" so the driver synthesizes both an
ASSERT and a CLEAR event (with the same timestamp for each). When the pulse
width is about equal to the interrupt latency the driver may intermittantly
see both edges of the pulse. To prevent generating spurious events, the
driver implements a half-second lockout period after generating an event
before it will generate another.

Differential Revision: https://reviews.freebsd.org/D4477

Use bus_alloc_resource_any(), rather than bus_alloc_resource()
with start 0 and end ~0. This avoids confusion WRT to what the
value of length can or should be.

Style fix, no functional changes -- do the braces for switches correctly.

Correct the polarity of the PPS assert and clear events with respect to the
electrical signals on the serial port. Virtually all devices which output a
PPS signal generate a brief higher-voltage pulse, the leading edge of which
is the on-time point.

Both DCD and CTS are active-low signals on the wire, meaning the assertion
of their status bits in the modem status register corresponds to the lower
voltage level on the wire. So when the status bit transitions to not-set,
create a PPS assert event; when the status bit transitions to set, create a
PPS clear event.

Allow the choice of PPS signal captured by uart(4) to be runtime-configured,
eliminating the need to build a custom kernel to use the CTS signal.

The historical UART_PPS_ON_CTS kernel option is still honored, but now it
can be overridden at runtime using a tunable to configure all uart devices
(hw.uart.pps_mode) or specific devices (dev.uart.#.pps_mode). The per-
device config is both a tunable and a writable sysctl.

This syncs the PPS capabilities of uart(4) with the enhancements recently
recently added to ucom(4) for capturing from USB serial devices.

Relnotes: yes

Provide the tty-layer mutex when initializing the pps api. This allows
time_pps_fetch() to be used in blocking mode.

Also, don't init the pps api for system devices (consoles) that provide a
custom attach routine. The device may actually be a keyboard or other non-
tty device. If it wants to do pps processing (unlikely) it must handle
everything for itself. (In reality, only a sun keyboard uses a custom
attach routine, and it doesn't make a good pps device.)

- Since r253161, uart_intr() abuses FILTER_SCHEDULE_THREAD for signaling
uart_bus_attach() during its test that 20 iterations weren't sufficient
for clearing all pending interrupts, assuming this means that hardware
is broken and doesn't deassert interrupts. However, under pressure, 20
iterations also can be insufficient for clearing all pending interrupts,
leading to a panic as intr_event_handle() tries to schedule an interrupt
handler not registered. Solve this by introducing a flag that is set in
test mode and otherwise restores pre-r253161 behavior of uart_intr(). The
approach of additionally registering uart_intr() as handler as suggested
in PR 194979 is not taken as that in turn would abuse special pccard and
pccbb handling code of intr_event_handle(). [1]
- Const'ify uart_driver_name.
- Fix some minor style bugs.

PR: 194979 [1]
Reviewed by: marcel (earlier version)
MFC after: 3 days

If uart interrupts are not functioning then schedule the callout to do the
polling at device attach time [1].

Add tunables 'debug.uart_force_poll' and 'debug.uart_poll_freq' to control
uart polling.

Submitted by: Aleksey Kuleshov (rndfax@yandex.ru) [1]

Add support for the uart classes to set their default register shift value.
This is needed with the pl011 driver. Before this change it would default
to a shift of 0, however the hardware places the registers at 4-byte
addresses meaning the value should be 2.

This patch fixes this for the pl011 when configured using the fdt. The
other drivers have a default value of 0 to keep this a no-op.

MFC after: 1 week

Back out r262921. I don't know what I was thinking, but it is lame.

Set the baud rate if it isn't 0 (meaning it has been specified) not
only if it is 0 (meaning that it hasn't been specified and is likely
to turn off the UART's transmitter).

Don't lock in the generic grab just to lock again in the specific grabs.
(I committed the wrong version of uart_core.c, which still had this).

Pointy hat: imp

Introduce grab and ungrab upcalls. When the kernel desires to grab the
console, it calls the grab functions. These functions should turn off
the RX interrupts, and any others that interfere. This makes mountroot
prompt work again. If there's more generalized need other than
prompting, many of these routines should be expanded to do those new
things.

Should have been part of r260889, but waasn't due to command line typo.

Reviewed by: bde (with reservations)

Allow UART_POLL_FREQ to be set as a kernel option as well as via tunable
(the code was already set up for this, just needs to be in conf/options).

Also, if reporting that polling is being used, report the frequency too.

Protect against broken hardware. In this particular case, protect against
H/W not de-asserting the interrupt at all. On x86, and because of the
following conditions, this results in a hard hang with interrupts disabled:
1. The uart(4) driver uses a spin lock to protect against concurrent
access to the H/W. Spin locks disable and restore interrupts.
2. Restoring the interrupt on x86 always writes the flags register. Even
if we're restoring the interrupt from disabled to disabled.
3. The x86 CPU has a short window in which interrupts are enabled when the
flags register is written.
4. The uart(4) driver registers a fast interrupt by default.

To catch this case, we first try to clear any pending H/W interrupts and in
particular, before setting up the interrupt. This makes sure the interrupt
is masked on the PIC. The interrupt handler now has a limit set on the
number of iterations it'll go through to clear interrupt conditions. If the
limit is hit, the handler will return FILTER_SCHEDULE_THREAD. The attach
function will check for this return code and avoid setting up the interrupt
and foce polling in that case.

Obtained from: Juniper Networks, Inc.

Fix several typos

PR: kern/176054
Submitted by: Christoph Mallon <christoph.mallon@gmx.de>
MFC after: 3 days

Accommodate uart devices with large FIFOs (or DMA buffers which amount
to the same thing) by allocating the uart(4) rx buffer based on the
device's rxfifosz rather than using a hard-coded size of 384 bytes.

The historical 384 byte size is 3 times the largest hard-coded fifo
size in the tree, so use that ratio as a guide and allocate the buffer
as three times rxfifosz, but never smaller than the historical size.

uart: add resume method and enable it for attachments on the most common
x86 buses

Otherwise the uart hardware could be in such a state after the resume
where IER is cleared and thus no interrupts are generated.

This behavior is observed and tested with QEMU, so I am comitting this
change to help with my debugging.
There has been no feedback from users of serial ports on real hardware.

MFC after: 20 days

Complete polled-mode operation by using a callout if the device will be
used in polled-mode. The callout invokes uart_intr, which rearms the timeout.
Implemented for bhyve, but generically useful for e.g. embedded bringup
when the interrupt controller hasn't been setup, or if it's not deemed
worthy to wire an interrupt line from a serial port.

Submitted by: neel
Reviewed by: marcel
Obtained from: NetApp
MFC after: 3 weeks

Mark MALLOC_DEFINEs static that have no corresponding MALLOC_DECLAREs.

This means that their use is restricted to a single C file.

Follow up to r225203 refining break-to-debugger run-time configuration
improvements:

(1) Implement new model in previously missed at91 UART driver
(2) Move BREAK_TO_DEBUGGER and ALT_BREAK_TO_DEBUGGER from opt_comconsole.h
to opt_kdb.h (spotted by np)
(3) Garbage collect now-unused opt_comconsole.h

MFC after: 3 weeks
Approved by: re (bz)

Attempt to make break-to-debugger and alternative break-to-debugger more
accessible:

(1) Always compile in support for breaking into the debugger if options
KDB is present in the kernel.

(2) Disable both by default, but allow them to be enabled via tunables
and sysctls debug.kdb.break_to_debugger and
debug.kdb.alt_break_to_debugger.

(3) options BREAK_TO_DEBUGGER and options ALT_BREAK_TO_DEBUGGER continue
to behave as before -- only now instead of compiling in
break-to-debugger support, they change the default values of the
above sysctls to enable those features by default. Current kernel
configurations should, therefore, continue to behave as expected.

(4) Migrate alternative break-to-debugger state machine logic out of
individual device drivers into centralised KDB code. This has a
number of upsides, but also one downside: it's now tricky to release
sio spin locks when entering the debugger, so we don't. However,
similar logic does not exist in other device drivers, including uart.

(5) dcons requires some special handling; unlike other console types, it
allows overriding KDB's own debugger selection, so we need a new
interface to KDB to allow that to work.

GENERIC kernels in -CURRENT will now support break-to-debugger as long as
appropriate boot/run-time options are set, which should improve the
debuggability of BETA kernels significantly.

MFC after: 3 weeks
Reviewed by: kib, nwhitehorn
Approved by: re (bz)

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Remove unneeded includes of <sys/termios.h>.

MFC change 197721:
Fix RTS/CTS flow control, broken by the TTY overhaul. The new TTY
interface is fairly simple WRT dealing with flow control, but
needed 2 new RX buffer functions with "get-char-from-buf" separated
from "advance-buf-pointer" so that the pointer could be advanced
only when ttydisc_rint() succeeded.

Approved by: re (kib)

Fix RTS/CTS flow control, broken by the TTY overhaul. The new TTY
interface is fairly simple WRT dealing with flow control, but
needed 2 new RX buffer functions with "get-char-from-buf" separated
from "advance-buf-pointer" so that the pointer could be advanced
only when ttydisc_rint() succeeded.

MFC after: 1 week

- Import the HEAD csup code which is the basis for the cvsmode work.

Integrate the new MPSAFE TTY layer to the FreeBSD operating system.

The last half year I've been working on a replacement TTY layer for the
FreeBSD kernel. The new TTY layer was designed to improve the following:

- Improved driver model:

The old TTY layer has a driver model that is not abstract enough to
make it friendly to use. A good example is the output path, where the
device drivers directly access the output buffers. This means that an
in-kernel PPP implementation must always convert network buffers into
TTY buffers.

If a PPP implementation would be built on top of the new TTY layer
(still needs a hooks layer, though), it would allow the PPP
implementation to directly hand the data to the TTY driver.

- Improved hotplugging:

With the old TTY layer, it isn't entirely safe to destroy TTY's from
the system. This implementation has a two-step destructing design,
where the driver first abandons the TTY. After all threads have left
the TTY, the TTY layer calls a routine in the driver, which can be
used to free resources (unit numbers, etc).

The pts(4) driver also implements this feature, which means
posix_openpt() will now return PTY's that are created on the fly.

- Improved performance:

One of the major improvements is the per-TTY mutex, which is expected
to improve scalability when compared to the old Giant locking.
Another change is the unbuffered copying to userspace, which is both
used on TTY device nodes and PTY masters.

Upgrading should be quite straightforward. Unlike previous versions,
existing kernel configuration files do not need to be changed, except
when they reference device drivers that are listed in UPDATING.

Obtained from: //depot/projects/mpsafetty/...
Approved by: philip (ex-mentor)
Discussed: on the lists, at BSDCan, at the DevSummit
Sponsored by: Snow B.V., the Netherlands
dcons(4) fixed by: kan

Expand kdb_alt_break a little, most commonly used with the option
ALT_BREAK_TO_DEBUGGER. In addition to "Enter ~ ctrl-B" (to enter the
debugger), there is now "Enter ~ ctrl-P" (force panic) and
"Enter ~ ctrl-R" (request clean reboot, ala ctrl-alt-del on syscons).

We've used variations of this at work. The force panic sequence is
best used with KDB_UNATTENDED for when you just want it to dump and
get on with it.

The reboot request is a safer way of getting into single user than
a power cycle. eg: you've hosed the ability to log in (pam, rtld, etc).
It gives init the reboot signal, which causes an orderly reboot.

I've taken my best guess at what the !x86 and non-sio code changes
should be.

This also makes sio release its spinlock before calling KDB/DDB.

Add a new 'why' argument to kdb_enter(), and a set of constants to use
for that argument. This will allow DDB to detect the broad category of
reason why the debugger has been entered, which it can use for the
purposes of deciding which DDB script to run.

Assign approximate why values to all current consumers of the
kdb_enter() interface.

Don't expose the uart_ops structure directly, but instead have
it obtained through the uart_class structure. This allows us
to declare the uart_class structure as weak and as such allows
us to reference it even when it's not compiled-in.
It also allows is to get the uart_ops structure by name, which
makes it possible to implement the dt tag handling in uart_getenv().
The side-effect of all this is that we're using the uart_class
structure more consistently which means that we now also have
access to the size of the bus space block needed by the hardware
when we map the bus space, eliminating any hardcoding.

When we match UARTs found during bus-enumeration with UARTs used for
system devices (i.e. console, debug port or keyboard), don't stop
after the first match. Find them all and keep track of the last.
The reason for this change is that the low-level console is always
added to the list of system devices first, with other devices added
later. Since new devices are added to the list at the head, we have
the console always at the end. When a debug port is using the same
UART as the console, we would previously mark the "newbus" UART as
a debug port instead of as a console. This would later result in a
panic because no "newbus" device was associated with the console.
By matching all possible system devices we would mark the "newbus"
UART as a console and not as a debug port.
While it is arguably better to be able to mark a "newbus" UART as
both console and debug port, this fix is lightweight and allows
a single UART to be used as the console as well as a debug port
with only the aesthetic bug of not telling the user about it also
being a debug port.

Now that we match all possible system devices, update the rclk of
the system devices with the rclk that was obtained through the
bus attachment. It is generally true that clock information is
more reliable when obtained from the parent bus than by means of
some hardcoded or assumed value used early in the boot. This by
virtue of having more context information.

MFC after: 1 month

o break newbus api: add a new argument of type driver_filter_t to
bus_setup_intr()

o add an int return code to all fast handlers

o retire INTR_FAST/IH_FAST

For more info: http://docs.freebsd.org/cgi/getmsg.cgi?fetch=465712+0+current/freebsd-current

Reviewed by: many
Approved by: re@

Implement the ipend() method of the serdev I/F.

Add support for scc(4).

Replace our local UART_SIGMASK_* with the global SER_MASK_*.

MFp4:
Stop using our local UART_IPEND_* and instead use the global SER_INT_*
as defined in <sys/serial.h>.

- Use bus_setup_intr() and bus_teardown_intr() to register device driver
interrupt handlers rather than BUS_SETUP_INTR() and BUS_TEARDOWN_INTR().
Uses of the BUS_*() versions in the implementation of foo_intr methods
in bus drivers were not changed. Mostly this just means that some
drivers might start printing diagnostic messages like [FAST] when
appropriate as well as honoring mpsafenet=0.
- Fix two more of the ppbus drivers' identify routines to function
correctly in the mythical case of a machine with more than one ppbus.

In uart_bus_probe() return BUS_PROBE_DEFAULT when the probe is
successful.

- Allocate the interrupt resource as RF_SHAREABLE allowing uart(4) to work
with shared IRQs in case the bus code, MD interrupt code, etc. permits.
Together with sys/sparc64/sparc64/intr_machdep.c rev. 1.21 this fixes
an endless loop in uart_intr() when using the second NS16550 on the ISA
bus of sparc64 machines.
- Destroy the hardware mutex on detach and in case attaching fails.

Approved by: marcel

Start each of the license/copyright comments with /*-, minor shuffle of lines

Add UART_IOCTL_BAUD to allow us to query the hardware about the
current baudrate setting. Use this ioctl() when we don't know the
baudrate of the sysdev (as represented by a 0 value). When the
ioctl() fails, e.g. when the backend hasn't implemented it or the
hardware doesn't provide the means to determine its current baudrate
setting, we invalidate the baudrate setting by setting it to -1.
None of the backends currently implement the new ioctl().

Update for the KDB framework:
o Call kdb_enter() instead of breakpoint().
o Call kdb_alt_break() instead of db_alt_break().
o Make debugging code conditional upon KDB instead of DDB.

When the interrupt cannot be INTR_FAST, it still is INTR_MPSAFE.
Mark it as such.

Convert callers to the new bus_alloc_resource_any(9) API.

Submitted by: Mark Santcroos <marks@ripe.net>
Reviewed by: imp, dfr, bde

Revert the introduction of iobase in struct uart_bas. Both the SAB82532
and the Z8530 drivers used the I/O address as a quick and dirty way to
determine which channel they operated on, but formalizing this by
introducing iobase is not a solution. How for example would a driver
know which channel it controls for a multi-channel UART that only has a
single I/O range?

Instead, add an explicit field, called chan, to struct uart_bas that
holds the channel within a device, or 0 otherwise. The chan field is
initialized both by the system device probing (i.e. a system console)
or it is passed down to uart_bus_probe() by any of the bus front-ends.
As such, it impacts all platforms and bus drivers and makes it a rather
large commit.

Remove the use of iobase in uart_cpu_eqres() for pc98. It is expected
that platforms have the capability to compare tag and handle pairs for
equality; as to determine whether two pairs access the same device or
not. The use of iobase for pc98 makes it impossible to formalize this
and turn it into a real newbus function later. This commit reverts
uart_cpu_eqres() for pc98 to an unimplemented function. It has to be
reimplemented using only the tag and handle fields in struct uart_bas.

Rewrite the SAB82532 and Z8530 drivers to use the chan field in struct
uart_bas. Remove the IS_CHANNEL_A and IS_CHANNEL_B macros. We don't
need to abstract anything anymore.

Discussed with: nyan
Tested on: i386, ia64, sparc64

Initialize iobase, bsh and bst.

- Keep the base address in struct uart_bas for sab82532 and z8530 modules.
- Remove buggy uart_cpu_busaddr() function.

In uart_intr() loop until all interrupts have been handled. Previously
an UART interface could get stuck when a new interrupt condition
arose while servicing a previous interrupt. Since an interrupt was
already pending, no new interrupt would be triggered.

Avoid infinite recursion by flushing the Rx FIFO and marking an
overrun condition when we could not move the data from the Rx
FIFO to the receive buffer in toto. Failure to flush the Rx FIFO
would leave the Rx ready condition pending.

Note that the SAB 82532 already did this due to the nature of the
chip.

Add locking to the hardware drivers. I intended to figure out more
precisely where locking would be needed before adding it, but it
seems uart(4) draws slightly too much attention to have it without
locking for too long.
The lock added is a spinlock that protects access to the underlying
hardware. As a first and obvious stab at this, each method of the
hardware interface grabs the lock. Roughly speaking this serializes
the methods. Exceptions are the probe, attach and detach methods.

Add support for using uart(4) for pulse capturing for the Pulse Per
Second (PPS) timing interface. The support is non-optional and by
default uses the DCD line signal as the pulse input. A compile-time
option (UART_PPS_ON_CTS) can be used to have uart(4) use the CTS line
signal.

Include <sys/timepps.h> in uart_bus.h to avoid having to add the
inclusion of that header in all source files.

Reviewed by: phk

The uart(4) driver is an universal driver for various UART hardware.
It improves on sio(4) in the following areas:
o Fully newbusified to allow for memory mapped I/O. This is a must
for ia64 and sparc64,
o Machine dependent code to take full advantage of machine and firm-
ware specific ways to define serial consoles and/or debug ports.
o Hardware abstraction layer to allow the driver to be used with
various UARTs, such as the well-known ns8250 family of UARTs, the
Siemens sab82532 or the Zilog Z8530. This is especially important
for pc98 and sparc64 where it's common to have different UARTs,
o The notion of system devices to unkludge low-level consoles and
remote gdb ports and provides the mechanics necessary to support
the keyboard on sparc64 (which is UART based).
o The notion of a kernel interface so that a UART can be tied to
something other than the well-known TTY interface. This is needed
on sparc64 to present the user with a device and ioctl handling
suitable for a keyboard, but also allows us to cleanly hide an
UART when used as a debug port.

Following is a list of features and bugs/flaws specific to the ns8250
family of UARTs as compared to their support in sio(4):
o The uart(4) driver determines the FIFO size and automaticly takes
advantages of larger FIFOs and/or additional features. Note that
since I don't have sufficient access to 16[679]5x UARTs, hardware
flow control has not been enabled. This is almost trivial to do,
provided one can test. The downside of this is that broken UARTs
are more likely to not work correctly with uart(4). The need for
tunables or knobs may be large enough to warrant their creation.
o The uart(4) driver does not share the same bumpy history as sio(4)
and will therefore not provide the necessary hooks, tweaks, quirks
or work-arounds to deal with once common hardware. To that extend,
uart(4) supports a subset of the UARTs that sio(4) supports. The
question before us is whether the subset is sufficient for current
hardware.
o There is no support for multiport UARTs in uart(4). The decision
behind this is that uart(4) deals with one EIA RS232-C interface.
Packaging of multiple interfaces in a single chip or on a single
expansion board is beyond the scope of uart(4) and is now mostly
left for puc(4) to deal with. Lack of hardware made it impossible
to actually implement such a dependency other than is present for
the dual channel SAB82532 and Z8350 SCCs.

The current list of missing features is:
o No configuration capabilities. A set of tunables and sysctls is
being worked out. There are likely not going to be any or much
compile-time knobs. Such configuration does not fit well with
current hardware.
o No support for the PPS API. This is partly dependent on the
ability to configure uart(4) and partly dependent on having
sufficient information to implement it properly.

As usual, the manpage is present but lacks the attention the
software has gotten.