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.

1 files changed, 726 insertions, 0 deletions

diff --git a/sys/dev/uart/uart_dev_ns8250.c b/sys/dev/uart/uart_dev_ns8250.c
new file mode 100644
index 0000000..d09371d
--- /dev/null
+++ b/sys/dev/uart/uart_dev_ns8250.c
@@ -0,0 +1,726 @@
+/*
+ * Copyright (c) 2003 Marcel Moolenaar
+ * All rights reserved.
+ *
+ * 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 ``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 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.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/bus.h>
+#include <sys/conf.h>
+#include <machine/bus.h>
+
+#include <dev/uart/uart.h>
+#include <dev/uart/uart_cpu.h>
+#include <dev/uart/uart_bus.h>
+#include <dev/uart/uart_dev_ns8250.h>
+
+#include "uart_if.h"
+
+#define	DEFAULT_RCLK	1843200
+
+/*
+ * Clear pending interrupts. THRE is cleared by reading IIR. Data
+ * that may have been received gets lost here.
+ */
+static void
+ns8250_clrint(struct uart_bas *bas)
+{
+	uint8_t iir;
+
+	iir = uart_getreg(bas, REG_IIR);
+	while ((iir & IIR_NOPEND) == 0) {
+		iir &= IIR_IMASK;
+		if (iir == IIR_RLS)
+			(void)uart_getreg(bas, REG_LSR);
+		else if (iir == IIR_RXRDY || iir == IIR_RXTOUT)
+			(void)uart_getreg(bas, REG_DATA);
+		else if (iir == IIR_MLSC)
+			(void)uart_getreg(bas, REG_MSR);
+		uart_barrier(bas);
+		iir = uart_getreg(bas, REG_IIR);
+	}
+}
+
+static int
+ns8250_delay(struct uart_bas *bas)
+{
+	int divisor;
+	u_char lcr;
+
+	lcr = uart_getreg(bas, REG_LCR);
+	uart_setreg(bas, REG_LCR, lcr | LCR_DLAB);
+	uart_barrier(bas);
+	divisor = uart_getdreg(bas, REG_DL);
+	uart_barrier(bas);
+	uart_setreg(bas, REG_LCR, lcr);
+	uart_barrier(bas);
+
+	/* 1/10th the time to transmit 1 character (estimate). */
+	return (16000000 * divisor / bas->rclk);
+}
+
+static int
+ns8250_divisor(int rclk, int baudrate)
+{
+	int actual_baud, divisor;
+	int error;
+
+	if (baudrate == 0)
+		return (0);
+
+	divisor = (rclk / (baudrate << 3) + 1) >> 1;
+	if (divisor == 0 || divisor >= 65536)
+		return (0);
+	actual_baud = rclk / (divisor << 4);
+
+	/* 10 times error in percent: */
+	error = ((actual_baud - baudrate) * 2000 / baudrate + 1) >> 1;
+
+	/* 3.0% maximum error tolerance: */
+	if (error < -30 || error > 30)
+		return (0);
+
+	return (divisor);
+}
+
+static int
+ns8250_drain(struct uart_bas *bas, int what)
+{
+	int delay, limit;
+
+	delay = ns8250_delay(bas);
+
+	if (what & UART_DRAIN_TRANSMITTER) {
+		/*
+		 * Pick an arbitrary high limit to avoid getting stuck in
+		 * an infinite loop when the hardware is broken. Make the
+		 * limit high enough to handle large FIFOs.
+		 */
+		limit = 10*1024;
+		while ((uart_getreg(bas, REG_LSR) & LSR_TEMT) == 0 && --limit)
+			DELAY(delay);
+		if (limit == 0) {
+			/* printf("ns8250: transmitter appears stuck... "); */
+			return (EIO);
+		}
+	}
+
+	if (what & UART_DRAIN_RECEIVER) {
+		/*
+		 * Pick an arbitrary high limit to avoid getting stuck in
+		 * an infinite loop when the hardware is broken. Make the
+		 * limit high enough to handle large FIFOs and integrated
+		 * UARTs. The HP rx2600 for example has 3 UARTs on the
+		 * management board that tend to get a lot of data send
+		 * to it when the UART is first activated.
+		 */
+		limit=10*4096;
+		while ((uart_getreg(bas, REG_LSR) & LSR_RXRDY) && --limit) {
+			(void)uart_getreg(bas, REG_DATA);
+			uart_barrier(bas);
+			DELAY(delay << 2);
+		}
+		if (limit == 0) {
+			/* printf("ns8250: receiver appears broken... "); */
+			return (EIO);
+		}
+	}
+
+	return (0);
+}
+
+/*
+ * We can only flush UARTs with FIFOs. UARTs without FIFOs should be
+ * drained. WARNING: this function clobbers the FIFO setting!
+ */
+static void
+ns8250_flush(struct uart_bas *bas, int what)
+{
+	uint8_t fcr;
+
+	fcr = FCR_ENABLE;
+	if (what & UART_FLUSH_TRANSMITTER)
+		fcr |= FCR_XMT_RST;
+	if (what & UART_FLUSH_RECEIVER)
+		fcr |= FCR_RCV_RST;
+	uart_setreg(bas, REG_FCR, fcr);
+	uart_barrier(bas);
+}
+
+static int
+ns8250_param(struct uart_bas *bas, int baudrate, int databits, int stopbits,
+    int parity)
+{
+	int divisor;
+	uint8_t lcr;
+
+	lcr = 0;
+	if (databits >= 8)
+		lcr |= LCR_8BITS;
+	else if (databits == 7)
+		lcr |= LCR_7BITS;
+	else if (databits == 6)
+		lcr |= LCR_6BITS;
+	else
+		lcr |= LCR_5BITS;
+	if (stopbits > 1)
+		lcr |= LCR_STOPB;
+	lcr |= parity << 3;
+
+	/* Set baudrate. */
+	if (baudrate > 0) {
+		uart_setreg(bas, REG_LCR, lcr | LCR_DLAB);
+		uart_barrier(bas);
+		divisor = ns8250_divisor(bas->rclk, baudrate);
+		if (divisor == 0)
+			return (EINVAL);
+		uart_setdreg(bas, REG_DL, divisor);
+		uart_barrier(bas);
+	}
+
+	/* Set LCR and clear DLAB. */
+	uart_setreg(bas, REG_LCR, lcr);
+	uart_barrier(bas);
+	return (0);
+}
+
+/*
+ * Low-level UART interface.
+ */
+static int ns8250_probe(struct uart_bas *bas);
+static void ns8250_init(struct uart_bas *bas, int, int, int, int);
+static void ns8250_term(struct uart_bas *bas);
+static void ns8250_putc(struct uart_bas *bas, int);
+static int ns8250_poll(struct uart_bas *bas);
+static int ns8250_getc(struct uart_bas *bas);
+
+struct uart_ops uart_ns8250_ops = {
+	.probe = ns8250_probe,
+	.init = ns8250_init,
+	.term = ns8250_term,
+	.putc = ns8250_putc,
+	.poll = ns8250_poll,
+	.getc = ns8250_getc,
+};
+
+static int
+ns8250_probe(struct uart_bas *bas)
+{
+	u_char lcr, val;
+
+	/* Check known 0 bits that don't depend on DLAB. */
+	val = uart_getreg(bas, REG_IIR);
+	if (val & 0x30)
+		return (ENXIO);
+	val = uart_getreg(bas, REG_MCR);
+	if (val & 0xe0)
+		return (ENXIO);
+
+	lcr = uart_getreg(bas, REG_LCR);
+	uart_setreg(bas, REG_LCR, lcr & ~LCR_DLAB);
+	uart_barrier(bas);
+
+	/* Check known 0 bits that depend on !DLAB. */
+	val = uart_getreg(bas, REG_IER);
+	if (val & 0xf0)
+		goto fail;
+
+	uart_setreg(bas, REG_LCR, lcr);
+	uart_barrier(bas);
+	return (0);
+
+ fail:
+	uart_setreg(bas, REG_LCR, lcr);
+	uart_barrier(bas);
+	return (ENXIO);
+}
+
+static void
+ns8250_init(struct uart_bas *bas, int baudrate, int databits, int stopbits,
+    int parity)
+{
+
+	if (bas->rclk == 0)
+		bas->rclk = DEFAULT_RCLK;
+	ns8250_param(bas, baudrate, databits, stopbits, parity);
+
+	/* Disable all interrupt sources. */
+	uart_setreg(bas, REG_IER, 0);
+	uart_barrier(bas);
+
+	/* Disable the FIFO (if present). */
+	uart_setreg(bas, REG_FCR, 0);
+	uart_barrier(bas);
+
+	/* Set RTS & DTR. */
+	uart_setreg(bas, REG_MCR, MCR_IE | MCR_RTS | MCR_DTR);
+	uart_barrier(bas);
+
+	ns8250_clrint(bas);
+}
+
+static void
+ns8250_term(struct uart_bas *bas)
+{
+
+	/* Clear RTS & DTR. */
+	uart_setreg(bas, REG_MCR, MCR_IE);
+	uart_barrier(bas);
+}
+
+static void
+ns8250_putc(struct uart_bas *bas, int c)
+{
+	int delay, limit;
+
+	/* 1/10th the time to transmit 1 character (estimate). */
+	delay = ns8250_delay(bas);
+
+	limit = 20;
+	while ((uart_getreg(bas, REG_LSR) & LSR_THRE) == 0 && --limit)
+		DELAY(delay);
+	uart_setreg(bas, REG_DATA, c);
+	limit = 40;
+	while ((uart_getreg(bas, REG_LSR) & LSR_TEMT) == 0 && --limit)
+		DELAY(delay);
+}
+
+static int
+ns8250_poll(struct uart_bas *bas)
+{
+
+	if (uart_getreg(bas, REG_LSR) & LSR_RXRDY)
+		return (uart_getreg(bas, REG_DATA));
+	return (-1);
+}
+
+static int
+ns8250_getc(struct uart_bas *bas)
+{
+	int delay;
+
+	/* 1/10th the time to transmit 1 character (estimate). */
+	delay = ns8250_delay(bas);
+
+	while ((uart_getreg(bas, REG_LSR) & LSR_RXRDY) == 0)
+		DELAY(delay);
+	return (uart_getreg(bas, REG_DATA));
+}
+
+/*
+ * High-level UART interface.
+ */
+struct ns8250_softc {
+	struct uart_softc base;
+	uint8_t		fcr;
+	uint8_t		ier;
+	uint8_t		mcr;
+};
+
+static int ns8250_bus_attach(struct uart_softc *);
+static int ns8250_bus_detach(struct uart_softc *);
+static int ns8250_bus_flush(struct uart_softc *, int);
+static int ns8250_bus_getsig(struct uart_softc *);
+static int ns8250_bus_ioctl(struct uart_softc *, int, intptr_t);
+static int ns8250_bus_ipend(struct uart_softc *);
+static int ns8250_bus_param(struct uart_softc *, int, int, int, int);
+static int ns8250_bus_probe(struct uart_softc *);
+static int ns8250_bus_receive(struct uart_softc *);
+static int ns8250_bus_setsig(struct uart_softc *, int);
+static int ns8250_bus_transmit(struct uart_softc *);
+
+static kobj_method_t ns8250_methods[] = {
+	KOBJMETHOD(uart_attach,		ns8250_bus_attach),
+	KOBJMETHOD(uart_detach,		ns8250_bus_detach),
+	KOBJMETHOD(uart_flush,		ns8250_bus_flush),
+	KOBJMETHOD(uart_getsig,		ns8250_bus_getsig),
+	KOBJMETHOD(uart_ioctl,		ns8250_bus_ioctl),
+	KOBJMETHOD(uart_ipend,		ns8250_bus_ipend),
+	KOBJMETHOD(uart_param,		ns8250_bus_param),
+	KOBJMETHOD(uart_probe,		ns8250_bus_probe),
+	KOBJMETHOD(uart_receive,	ns8250_bus_receive),
+	KOBJMETHOD(uart_setsig,		ns8250_bus_setsig),
+	KOBJMETHOD(uart_transmit,	ns8250_bus_transmit),
+	{ 0, 0 }
+};
+
+struct uart_class uart_ns8250_class = {
+	"ns8250 class",
+	ns8250_methods,
+	sizeof(struct ns8250_softc),
+	.uc_range = 8,
+	.uc_rclk = DEFAULT_RCLK
+};
+
+#define	SIGCHG(c, i, s, d)				\
+	if (c) {					\
+		i |= (i & s) ? s : s | d;		\
+	} else {					\
+		i = (i & s) ? (i & ~s) | d : i;		\
+	}
+
+static int
+ns8250_bus_attach(struct uart_softc *sc)
+{
+	struct ns8250_softc *ns8250 = (struct ns8250_softc*)sc;
+	struct uart_bas *bas;
+
+	bas = &sc->sc_bas;
+
+	ns8250->mcr = uart_getreg(bas, REG_MCR);
+	ns8250->fcr = FCR_ENABLE | FCR_RX_MEDH;
+	uart_setreg(bas, REG_FCR, ns8250->fcr);
+	uart_barrier(bas);
+	ns8250_bus_flush(sc, UART_FLUSH_RECEIVER|UART_FLUSH_TRANSMITTER);
+
+	if (ns8250->mcr & MCR_DTR)
+		sc->sc_hwsig |= UART_SIG_DTR;
+	if (ns8250->mcr & MCR_RTS)
+		sc->sc_hwsig |= UART_SIG_RTS;
+	ns8250_bus_getsig(sc);
+
+	ns8250_clrint(bas);
+	ns8250->ier = IER_EMSC | IER_ERLS | IER_ERXRDY;
+	uart_setreg(bas, REG_IER, ns8250->ier);
+	uart_barrier(bas);
+	return (0);
+}
+
+static int
+ns8250_bus_detach(struct uart_softc *sc)
+{
+	struct uart_bas *bas;
+
+	bas = &sc->sc_bas;
+	uart_setreg(bas, REG_IER, 0);
+	uart_barrier(bas);
+	ns8250_clrint(bas);
+	return (0);
+}
+
+static int
+ns8250_bus_flush(struct uart_softc *sc, int what)
+{
+	struct ns8250_softc *ns8250 = (struct ns8250_softc*)sc;
+	struct uart_bas *bas;
+
+	bas = &sc->sc_bas;
+	if (sc->sc_hasfifo) {
+		ns8250_flush(bas, what);
+		uart_setreg(bas, REG_FCR, ns8250->fcr);
+		uart_barrier(bas);
+		return (0);
+	}
+	return (ns8250_drain(bas, what));
+}
+
+static int
+ns8250_bus_getsig(struct uart_softc *sc)
+{
+	uint32_t new, old, sig;
+	uint8_t msr;
+
+	do {
+		old = sc->sc_hwsig;
+		sig = old;
+		msr = uart_getreg(&sc->sc_bas, REG_MSR);
+		SIGCHG(msr & MSR_DSR, sig, UART_SIG_DSR, UART_SIG_DDSR);
+		SIGCHG(msr & MSR_CTS, sig, UART_SIG_CTS, UART_SIG_DCTS);
+		SIGCHG(msr & MSR_DCD, sig, UART_SIG_DCD, UART_SIG_DDCD);
+		SIGCHG(msr & MSR_RI,  sig, UART_SIG_RI,  UART_SIG_DRI);
+		new = sig & ~UART_SIGMASK_DELTA;
+	} while (!atomic_cmpset_32(&sc->sc_hwsig, old, new));
+	return (sig);
+}
+
+static int
+ns8250_bus_ioctl(struct uart_softc *sc, int request, intptr_t data)
+{
+	struct uart_bas *bas;
+	uint8_t lcr;
+
+	bas = &sc->sc_bas;
+	switch (request) {
+	case UART_IOCTL_BREAK:
+		lcr = uart_getreg(bas, REG_LCR);
+		if (data)
+			lcr |= LCR_SBREAK;
+		else
+			lcr &= ~LCR_SBREAK;
+		uart_setreg(bas, REG_LCR, lcr);
+		uart_barrier(bas);
+		break;
+	default:
+		return (EINVAL);
+	}
+	return (0);
+}
+
+static int
+ns8250_bus_ipend(struct uart_softc *sc)
+{
+	struct uart_bas *bas;
+	int ipend;
+	uint8_t iir, lsr;
+
+	bas = &sc->sc_bas;
+	iir = uart_getreg(bas, REG_IIR);
+	if (iir & IIR_NOPEND)
+		return (0);
+
+	ipend = 0;
+	if (iir & IIR_RXRDY) {
+		lsr = uart_getreg(bas, REG_LSR);
+		if (lsr & LSR_OE)
+			ipend |= UART_IPEND_OVERRUN;
+		if (lsr & LSR_BI)
+			ipend |= UART_IPEND_BREAK;
+		if (lsr & LSR_RXRDY)
+			ipend |= UART_IPEND_RXREADY;
+	} else {
+		if (iir & IIR_TXRDY)
+			ipend |= UART_IPEND_TXIDLE;
+		else
+			ipend |= UART_IPEND_SIGCHG;
+	}
+
+	return ((sc->sc_leaving) ? 0 : ipend);
+}
+
+static int
+ns8250_bus_param(struct uart_softc *sc, int baudrate, int databits,
+    int stopbits, int parity)
+{
+	struct uart_bas *bas;
+
+	bas = &sc->sc_bas;
+	return (ns8250_param(bas, baudrate, databits, stopbits, parity));
+}
+
+static int
+ns8250_bus_probe(struct uart_softc *sc)
+{
+	struct uart_bas *bas;
+	int count, delay, error, limit;
+	uint8_t mcr;
+
+	bas = &sc->sc_bas;
+
+	error = ns8250_probe(bas);
+	if (error)
+		return (error);
+
+	mcr = MCR_IE;
+	if (sc->sc_sysdev == NULL) {
+		/* By using ns8250_init() we also set DTR and RTS. */
+		ns8250_init(bas, 9600, 8, 1, UART_PARITY_NONE);
+	} else
+		mcr |= MCR_DTR | MCR_RTS;
+
+	error = ns8250_drain(bas, UART_DRAIN_TRANSMITTER);
+	if (error)
+		return (error);
+
+	/*
+	 * Set loopback mode. This avoids having garbage on the wire and
+	 * also allows us send and receive data. We set DTR and RTS to
+	 * avoid the possibility that automatic flow-control prevents
+	 * any data from being sent. We clear IE to avoid raising interrupts.
+	 */
+	uart_setreg(bas, REG_MCR, MCR_LOOPBACK | MCR_DTR | MCR_RTS);
+	uart_barrier(bas);
+
+	/*
+	 * Enable FIFOs. And check that the UART has them. If not, we're
+	 * done. Otherwise we set DMA mode with the highest trigger level
+	 * so that we can determine the FIFO size. Since this is the first
+	 * time we enable the FIFOs, we reset them.
+	 */
+	uart_setreg(bas, REG_FCR, FCR_ENABLE);
+	uart_barrier(bas);
+	sc->sc_hasfifo = (uart_getreg(bas, REG_IIR) & IIR_FIFO_MASK) ? 1 : 0;
+	if (!sc->sc_hasfifo) {
+		/*
+		 * NS16450 or INS8250. We don't bother to differentiate
+		 * between them. They're too old to be interesting.
+		 */
+		uart_setreg(bas, REG_MCR, mcr);
+		uart_barrier(bas);
+		device_set_desc(sc->sc_dev, "8250 or 16450 or compatible");
+		return (0);
+	}
+
+	uart_setreg(bas, REG_FCR, FCR_ENABLE | FCR_DMA | FCR_RX_HIGH |
+	    FCR_XMT_RST | FCR_RCV_RST);
+	uart_barrier(bas);
+
+	count = 0;
+	delay = ns8250_delay(bas);
+
+	/* We have FIFOs. Drain the transmitter and receiver. */
+	error = ns8250_drain(bas, UART_DRAIN_RECEIVER|UART_DRAIN_TRANSMITTER);
+	if (error) {
+		uart_setreg(bas, REG_MCR, mcr);
+		uart_setreg(bas, REG_FCR, 0);
+		uart_barrier(bas);
+		goto describe;
+	}
+
+	uart_setreg(bas, REG_IER, IER_ERXRDY);
+	uart_barrier(bas);
+
+	/*
+	 * We should have a sufficiently clean "pipe" to determine the
+	 * size of the FIFOs. We send as much characters as is reasonable
+	 * and wait for the the RX interrupt to be asserted, counting the
+	 * characters as we send them. Based on that count we know the
+	 * FIFO size.
+	 */
+	while ((uart_getreg(bas, REG_IIR) & IIR_RXRDY) == 0 && count < 1030) {
+		uart_setreg(bas, REG_DATA, 0);
+		uart_barrier(bas);
+		count++;
+
+		limit = 30;
+		while ((uart_getreg(bas, REG_LSR) & LSR_TEMT) == 0 && --limit)
+			DELAY(delay);
+		if (limit == 0) {
+			uart_setreg(bas, REG_IER, 0);
+			uart_setreg(bas, REG_MCR, mcr);
+			uart_setreg(bas, REG_FCR, 0);
+			uart_barrier(bas);
+			count = 0;
+			goto describe;
+		}
+	}
+
+	uart_setreg(bas, REG_IER, 0);
+	uart_setreg(bas, REG_MCR, mcr);
+
+	/* Reset FIFOs. */
+	ns8250_flush(bas, UART_FLUSH_RECEIVER|UART_FLUSH_TRANSMITTER);
+
+ describe:
+	if (count >= 14 && count < 16) {
+		sc->sc_rxfifosz = 16;
+		device_set_desc(sc->sc_dev, "16550 or compatible");
+	} else if (count >= 28 && count < 32) {
+		sc->sc_rxfifosz = 32;
+		device_set_desc(sc->sc_dev, "16650 or compatible");
+	} else if (count >= 56 && count < 64) {
+		sc->sc_rxfifosz = 64;
+		device_set_desc(sc->sc_dev, "16750 or compatible");
+	} else if (count >= 112 && count < 128) {
+		sc->sc_rxfifosz = 128;
+		device_set_desc(sc->sc_dev, "16950 or compatible");
+	} else {
+		sc->sc_rxfifosz = 1;
+		device_set_desc(sc->sc_dev,
+		    "Non-standard ns8250 class UART with FIFOs");
+	}
+
+	/*
+	 * Force the Tx FIFO size to 16 bytes for now. We don't program the
+	 * Tx trigger. Also, we assume that all data has been sent when the
+	 * interrupt happens.
+	 */
+	sc->sc_txfifosz = 16;
+
+	return (0);
+}
+
+static int
+ns8250_bus_receive(struct uart_softc *sc)
+{
+	struct uart_bas *bas;
+	int xc;
+	uint8_t lsr;
+
+	bas = &sc->sc_bas;
+	while (!uart_rx_full(sc)) {
+		lsr = uart_getreg(bas, REG_LSR);
+		if ((lsr & LSR_RXRDY) == 0)
+			break;
+		xc = uart_getreg(bas, REG_DATA);
+		if (lsr & LSR_FE)
+			xc |= UART_STAT_FRAMERR;
+		if (lsr & LSR_PE)
+			xc |= UART_STAT_PARERR;
+		uart_rx_put(sc, xc);
+	}
+ 	return (0);
+}
+
+static int
+ns8250_bus_setsig(struct uart_softc *sc, int sig)
+{
+	struct ns8250_softc *ns8250 = (struct ns8250_softc*)sc;
+	struct uart_bas *bas;
+	uint32_t new, old;
+
+	bas = &sc->sc_bas;
+	do {
+		old = sc->sc_hwsig;
+		new = old;
+		if (sig & UART_SIG_DDTR) {
+			SIGCHG(sig & UART_SIG_DTR, new, UART_SIG_DTR,
+			    UART_SIG_DDTR);
+		}
+		if (sig & UART_SIG_DRTS) {
+			SIGCHG(sig & UART_SIG_RTS, new, UART_SIG_RTS,
+			    UART_SIG_DRTS);
+		}
+	} while (!atomic_cmpset_32(&sc->sc_hwsig, old, new));
+	ns8250->mcr &= ~(MCR_DTR|MCR_RTS);
+	if (new & UART_SIG_DTR)
+		ns8250->mcr |= MCR_DTR;
+	if (new & UART_SIG_RTS)
+		ns8250->mcr |= MCR_RTS;
+	uart_setreg(bas, REG_MCR, ns8250->mcr);
+	uart_barrier(bas);
+	return (0);
+}
+
+static int
+ns8250_bus_transmit(struct uart_softc *sc)
+{
+	struct ns8250_softc *ns8250 = (struct ns8250_softc*)sc;
+	struct uart_bas *bas;
+	int i;
+
+	bas = &sc->sc_bas;
+	while ((uart_getreg(bas, REG_LSR) & LSR_THRE) == 0)
+		;
+	uart_setreg(bas, REG_IER, ns8250->ier | IER_ETXRDY);
+	uart_barrier(bas);
+	for (i = 0; i < sc->sc_txdatasz; i++) {
+		uart_setreg(bas, REG_DATA, sc->sc_txbuf[i]);
+		uart_barrier(bas);
+	}
+	sc->sc_txbusy = 1;
+	return (0);
+}