Index: stand/i386/boot2/sio.S
===================================================================
--- stand/i386/boot2/sio.S
+++ stand/i386/boot2/sio.S
@@ -15,9 +15,12 @@
  * $FreeBSD$
  */
 
-		.set SIO_PRT,SIOPRT		# Base port
 		.set SIO_FMT,SIOFMT		# 8N1
 
+/* int sio_port */
+sio_port:	.long SIOPRT			# Base port
+
+		.globl sio_port
 		.globl sio_init
 		.globl sio_flush
 		.globl sio_putc
@@ -27,13 +30,15 @@
 /* int sio_init(int div) */
 
 sio_init:	pushl %eax
-		movw $SIO_PRT+0x3,%dx		# Data format reg
+		movl (sio_port),%edx
+		addl $0x3,%edx			# Data format reg
 		movb $SIO_FMT|0x80,%al		# Set format
 		outb %al,(%dx)			#  and DLAB
 		subb $0x3,%dl			# Divisor latch reg
 		popl %eax
 		outw %ax,(%dx)			#  BPS
-		movw $SIO_PRT+0x3,%dx		# Data format reg
+		movl (sio_port),%edx
+		addl $0x3,%edx			# Data format reg
 		movb $SIO_FMT,%al		# Clear
 		outb %al,(%dx)			#  DLAB
 		incl %edx			# Modem control reg
@@ -55,7 +60,8 @@
 /* void sio_putc(int c) */
 
 sio_putc:	pushl %eax
-		movw $SIO_PRT+0x5,%dx		# Line status reg
+		movl (sio_port),%edx
+		addl $0x5,%edx			# Line status reg
 		xor %ecx,%ecx			# Timeout
 		movb $0x40,%ch			#  counter
 sio_putc.1:	inb (%dx),%al			# Transmitter
@@ -77,7 +83,8 @@
 
 /* int sio_ischar(void) */
 
-sio_ischar:	movw $SIO_PRT+0x5,%dx		# Line status register
+sio_ischar:	movl (sio_port),%edx
+		addl $0x5,%edx			# Line status register
 		xorl %eax,%eax			# Zero
 		inb (%dx),%al			# Received data
 		andb $0x1,%al			#  ready?
Index: stand/i386/libi386/biosacpi.c
===================================================================
--- stand/i386/libi386/biosacpi.c
+++ stand/i386/libi386/biosacpi.c
@@ -38,6 +38,7 @@
 #define ACPI_SYSTEM_XFACE
 #include "actypes.h"
 #include "actbl.h"
+#include "actbl3.h"
 
 /*
  * Detect ACPI and export information about the ACPI BIOS into the
@@ -49,6 +50,93 @@
 
 #define RSDP_CHECKSUM_LENGTH 20
 
+static ACPI_TABLE_SPCR *
+find_spcr(ACPI_TABLE_RSDP *rsdp)
+{
+	unsigned count, i;
+	ACPI_TABLE_XSDT *xsdt;
+	ACPI_TABLE_RSDT *rsdt;
+	void *ptr;
+
+	if (rsdp->Revision >= 2 && rsdp->XsdtPhysicalAddress != 0) {
+		xsdt = (ACPI_TABLE_XSDT *)PTOV(rsdp->XsdtPhysicalAddress);
+
+		count = xsdt->Header.Length - sizeof(ACPI_TABLE_HEADER);
+		count /= sizeof(xsdt->TableOffsetEntry[0]);
+		for (i = 0; i < count; i++) {
+			ptr = PTOV(xsdt->TableOffsetEntry[i]);
+			if (memcmp(ptr, ACPI_SIG_SPCR,
+			    sizeof(ACPI_SIG_SPCR) - 1) == 0) {
+				return (ptr);
+			}
+		}
+	}
+	if (rsdp->RsdtPhysicalAddress != 0) {
+		rsdt = (ACPI_TABLE_RSDT *)PTOV(rsdp->RsdtPhysicalAddress);
+
+		count = rsdt->Header.Length - sizeof(ACPI_TABLE_HEADER);
+		count /= sizeof(rsdt->TableOffsetEntry[0]);
+		for (i = 0; i < count; i++) {
+			ptr = PTOV(rsdt->TableOffsetEntry[i]);
+			if (memcmp(ptr, ACPI_SIG_SPCR,
+			    sizeof(ACPI_SIG_SPCR) - 1) == 0) {
+				return (ptr);
+			}
+		}
+	}
+	return (NULL);
+}
+
+/*
+ * Find and parse SPCR table to set up serial console.
+ */
+static void
+biosacpi_setup_spcr(ACPI_TABLE_SPCR *spcr)
+{
+	unsigned baudrate;
+	char value[21];
+
+	if (spcr == NULL)
+		return;
+
+	switch (spcr->BaudRate) {
+	case 0:
+		baudrate = 0;
+		break;
+	case 3:
+		baudrate = 9600;
+		break;
+	case 4:
+		baudrate = 19200;
+		break;
+	case 6:
+		baudrate = 57600;
+		break;
+	case 7:
+		baudrate = 115200;
+		break;
+	default:
+		return;
+	}
+
+	switch (spcr->SerialPort.SpaceId) {
+	case ACPI_ADR_SPACE_SYSTEM_IO:
+		setenv("console", "comconsole", 1);
+		snprintf(value, sizeof(value), "%ju",
+		    (uintmax_t)spcr->SerialPort.Address);
+		setenv("comconsole_port", value, 1);
+		break;
+	default:
+		/* XXX not implemented. */
+		return;
+	}
+
+	if (baudrate > 0) {
+		snprintf(value, sizeof(value), "%u", baudrate);
+		setenv("comconsole_speed", value, 1);
+	}
+}
+
 void
 biosacpi_detect(void)
 {
@@ -95,6 +183,7 @@
 	setenv("hint.acpi.0.xsdt_length", buf, 1);
 	setenv("acpi.xsdt_length", buf, 1);
     }
+    biosacpi_setup_spcr(find_spcr(rsdp));
 }
 
 /*
Index: stand/i386/zfsboot/zfsboot.c
===================================================================
--- stand/i386/zfsboot/zfsboot.c
+++ stand/i386/zfsboot/zfsboot.c
@@ -106,6 +106,8 @@
 
 static const unsigned char dev_maj[NDEV] = {30, 4, 2};
 
+extern int sio_port;
+
 static struct i386_devdesc *bdev;
 static char cmd[512];
 static char cmddup[512];
@@ -169,6 +171,7 @@
 	unsigned i;
 	int auto_boot, fd, nextboot = 0;
 	struct disk_devdesc devdesc;
+	char *ptr;
 
 	bios_getmem();
 
@@ -182,6 +185,27 @@
 	}
 	setheap(heap_bottom, heap_top);
 
+	/*
+	 * detect ACPI for future reference. This may set console to comconsole
+	 * if we do have ACPI SPCR table.
+	 */
+        biosacpi_detect();
+	ptr = getenv("console");
+	if (ptr != NULL && strcmp(ptr, "comconsole") == 0) {
+		ioctrl = IO_SERIAL;
+
+		ptr = getenv("comconsole_port");
+		if (ptr != NULL)
+			sio_port = strtoul(ptr, NULL, 0);
+
+		ptr = getenv("comconsole_speed");
+		if (ptr != NULL) {
+			comspeed = strtoul(ptr, NULL, 0);
+			if (sio_init(115200 / comspeed) != 0)
+				ioctrl |= IO_KEYBOARD;
+		}
+	}
+
 	/*
 	 * Initialise the block cache. Set the upper limit.
 	 */