ISA device drivers use the ISA source interrupt number in locations where

the low level interrupt handler number should be used.  Change
setup_apic_irq_mapping() to allocate low level interrupt handler X (Xintr${X})
for any ISA interrupt X mentioned in the MP table.

Remove an assumption in the driver for the system clock (clock.c) that
interrupts mentioned in the MP table as delivered to IOAPIC #0 intpin Y
is handled by low level interrupt handler Y (Xintr${Y}) but don't assume
that low level interrupt handler 0 (Xintr0) is used.

Don't allocate two low level interrupt handlers for the system clock.
Reviewed by:	NOKUBI Hirotaka <hnokubi@yyy.or.jp>

15 files changed, 589 insertions, 87 deletions

diff --git a/sys/amd64/amd64/mp_machdep.c b/sys/amd64/amd64/mp_machdep.c
index b565cee..48d716a 100644
--- a/sys/amd64/amd64/mp_machdep.c
+++ b/sys/amd64/amd64/mp_machdep.c
@@ -335,6 +335,7 @@ static void	init_locks(void);
 static int	start_all_aps(u_int boot_addr);
 static void	install_ap_tramp(u_int boot_addr);
 static int	start_ap(int logicalCpu, u_int boot_addr);
+static int	apic_int_is_bus_type(int intr, int bus_type);
 
 /*
  * Calculate usable address in base memory for AP trampoline code.
@@ -960,7 +961,7 @@ mptable_pass2(void)
 }
 
 
-static void
+void
 assign_apic_irq(int apic, int intpin, int irq)
 {
 	int x;
@@ -983,6 +984,34 @@ assign_apic_irq(int apic, int intpin, int irq)
 	}
 }
 
+void
+revoke_apic_irq(int irq)
+{
+	int x;
+	int oldapic;
+	int oldintpin;
+	
+	if (int_to_apicintpin[irq].ioapic == -1)
+		panic("assign_apic_irq: inconsistent table");
+	
+	oldapic = int_to_apicintpin[irq].ioapic;
+	oldintpin = int_to_apicintpin[irq].int_pin;
+
+	int_to_apicintpin[irq].ioapic = -1;
+	int_to_apicintpin[irq].int_pin = 0;
+	int_to_apicintpin[irq].apic_address = NULL;
+	int_to_apicintpin[irq].redirindex = 0;
+	
+	for (x = 0; x < nintrs; x++) {
+		if ((io_apic_ints[x].int_type == 0 || 
+		     io_apic_ints[x].int_type == 3) &&
+		    io_apic_ints[x].int_vector == 0xff &&
+		    io_apic_ints[x].dst_apic_id == IO_TO_ID(oldapic) &&
+		    io_apic_ints[x].dst_apic_int == oldintpin)
+			io_apic_ints[x].int_vector = 0xff;
+	}
+}
+
 /*
  * parse an Intel MP specification table
  */
@@ -1049,37 +1078,66 @@ fix_mp_table(void)
 }
 
 
+/* Assign low level interrupt handlers */
 static void
 setup_apic_irq_mapping(void)
 {
 	int	x;
 	int	int_vector;
 
-	/* Assign low level interrupt handlers */
+	/* Clear array */
 	for (x = 0; x < APIC_INTMAPSIZE; x++) {
 		int_to_apicintpin[x].ioapic = -1;
 		int_to_apicintpin[x].int_pin = 0;
 		int_to_apicintpin[x].apic_address = NULL;
 		int_to_apicintpin[x].redirindex = 0;
 	}
+
+	/* First assign ISA/EISA interrupts */
+	for (x = 0; x < nintrs; x++) {
+		int_vector = io_apic_ints[x].src_bus_irq;
+		if (int_vector < APIC_INTMAPSIZE &&
+		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
+		    (apic_int_is_bus_type(x, ISA) ||
+		     apic_int_is_bus_type(x, EISA)) &&
+		    io_apic_ints[x].int_type == 0) {
+			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id), 
+					io_apic_ints[x].dst_apic_int,
+					int_vector);
+		}
+	}
+
+	/* Assign interrupts on first 24 intpins on IOAPIC #0 */
 	for (x = 0; x < nintrs; x++) {
-		if (io_apic_ints[x].dst_apic_int < APIC_INTMAPSIZE &&
+		int_vector = io_apic_ints[x].dst_apic_int;
+		if (int_vector < APIC_INTMAPSIZE &&
 		    io_apic_ints[x].dst_apic_id == IO_TO_ID(0) &&
 		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
 		    (io_apic_ints[x].int_type == 0 ||
 		     io_apic_ints[x].int_type == 3)) {
-			assign_apic_irq(0, 
+			assign_apic_irq(0,
 					io_apic_ints[x].dst_apic_int,
-					io_apic_ints[x].dst_apic_int);
+					int_vector);
 		}
 	}
+	/* 
+	 * Assign interrupts for remaining intpins.
+	 * Skip IOAPIC #0 intpin 0 if the type is ExtInt, since this indicates
+	 * that an entry for ISA/EISA irq 0 exist, and a fallback to mixed mode
+	 * due to 8254 interrupts not being delivered can reuse that low level
+	 * interrupt handler.
+	 */
 	int_vector = 0;
 	while (int_vector < APIC_INTMAPSIZE &&
 	       int_to_apicintpin[int_vector].ioapic != -1)
 		int_vector++;
 	for (x = 0; x < nintrs && int_vector < APIC_INTMAPSIZE; x++) {
 		if ((io_apic_ints[x].int_type == 0 ||
-		     io_apic_ints[x].int_type == 3) &&
+		     (io_apic_ints[x].int_type == 3 &&
+		      (io_apic_ints[x].dst_apic_id != IO_TO_ID(0) ||
+		       io_apic_ints[x].dst_apic_int != 0))) &&
 		    io_apic_ints[x].int_vector == 0xff) {
 			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id),
 					io_apic_ints[x].dst_apic_int,
diff --git a/sys/amd64/amd64/mptable.c b/sys/amd64/amd64/mptable.c
index b565cee..48d716a 100644
--- a/sys/amd64/amd64/mptable.c
+++ b/sys/amd64/amd64/mptable.c
@@ -335,6 +335,7 @@ static void	init_locks(void);
 static int	start_all_aps(u_int boot_addr);
 static void	install_ap_tramp(u_int boot_addr);
 static int	start_ap(int logicalCpu, u_int boot_addr);
+static int	apic_int_is_bus_type(int intr, int bus_type);
 
 /*
  * Calculate usable address in base memory for AP trampoline code.
@@ -960,7 +961,7 @@ mptable_pass2(void)
 }
 
 
-static void
+void
 assign_apic_irq(int apic, int intpin, int irq)
 {
 	int x;
@@ -983,6 +984,34 @@ assign_apic_irq(int apic, int intpin, int irq)
 	}
 }
 
+void
+revoke_apic_irq(int irq)
+{
+	int x;
+	int oldapic;
+	int oldintpin;
+	
+	if (int_to_apicintpin[irq].ioapic == -1)
+		panic("assign_apic_irq: inconsistent table");
+	
+	oldapic = int_to_apicintpin[irq].ioapic;
+	oldintpin = int_to_apicintpin[irq].int_pin;
+
+	int_to_apicintpin[irq].ioapic = -1;
+	int_to_apicintpin[irq].int_pin = 0;
+	int_to_apicintpin[irq].apic_address = NULL;
+	int_to_apicintpin[irq].redirindex = 0;
+	
+	for (x = 0; x < nintrs; x++) {
+		if ((io_apic_ints[x].int_type == 0 || 
+		     io_apic_ints[x].int_type == 3) &&
+		    io_apic_ints[x].int_vector == 0xff &&
+		    io_apic_ints[x].dst_apic_id == IO_TO_ID(oldapic) &&
+		    io_apic_ints[x].dst_apic_int == oldintpin)
+			io_apic_ints[x].int_vector = 0xff;
+	}
+}
+
 /*
  * parse an Intel MP specification table
  */
@@ -1049,37 +1078,66 @@ fix_mp_table(void)
 }
 
 
+/* Assign low level interrupt handlers */
 static void
 setup_apic_irq_mapping(void)
 {
 	int	x;
 	int	int_vector;
 
-	/* Assign low level interrupt handlers */
+	/* Clear array */
 	for (x = 0; x < APIC_INTMAPSIZE; x++) {
 		int_to_apicintpin[x].ioapic = -1;
 		int_to_apicintpin[x].int_pin = 0;
 		int_to_apicintpin[x].apic_address = NULL;
 		int_to_apicintpin[x].redirindex = 0;
 	}
+
+	/* First assign ISA/EISA interrupts */
+	for (x = 0; x < nintrs; x++) {
+		int_vector = io_apic_ints[x].src_bus_irq;
+		if (int_vector < APIC_INTMAPSIZE &&
+		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
+		    (apic_int_is_bus_type(x, ISA) ||
+		     apic_int_is_bus_type(x, EISA)) &&
+		    io_apic_ints[x].int_type == 0) {
+			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id), 
+					io_apic_ints[x].dst_apic_int,
+					int_vector);
+		}
+	}
+
+	/* Assign interrupts on first 24 intpins on IOAPIC #0 */
 	for (x = 0; x < nintrs; x++) {
-		if (io_apic_ints[x].dst_apic_int < APIC_INTMAPSIZE &&
+		int_vector = io_apic_ints[x].dst_apic_int;
+		if (int_vector < APIC_INTMAPSIZE &&
 		    io_apic_ints[x].dst_apic_id == IO_TO_ID(0) &&
 		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
 		    (io_apic_ints[x].int_type == 0 ||
 		     io_apic_ints[x].int_type == 3)) {
-			assign_apic_irq(0, 
+			assign_apic_irq(0,
 					io_apic_ints[x].dst_apic_int,
-					io_apic_ints[x].dst_apic_int);
+					int_vector);
 		}
 	}
+	/* 
+	 * Assign interrupts for remaining intpins.
+	 * Skip IOAPIC #0 intpin 0 if the type is ExtInt, since this indicates
+	 * that an entry for ISA/EISA irq 0 exist, and a fallback to mixed mode
+	 * due to 8254 interrupts not being delivered can reuse that low level
+	 * interrupt handler.
+	 */
 	int_vector = 0;
 	while (int_vector < APIC_INTMAPSIZE &&
 	       int_to_apicintpin[int_vector].ioapic != -1)
 		int_vector++;
 	for (x = 0; x < nintrs && int_vector < APIC_INTMAPSIZE; x++) {
 		if ((io_apic_ints[x].int_type == 0 ||
-		     io_apic_ints[x].int_type == 3) &&
+		     (io_apic_ints[x].int_type == 3 &&
+		      (io_apic_ints[x].dst_apic_id != IO_TO_ID(0) ||
+		       io_apic_ints[x].dst_apic_int != 0))) &&
 		    io_apic_ints[x].int_vector == 0xff) {
 			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id),
 					io_apic_ints[x].dst_apic_int,
diff --git a/sys/amd64/amd64/tsc.c b/sys/amd64/amd64/tsc.c
index 11b1426..ea39018 100644
--- a/sys/amd64/amd64/tsc.c
+++ b/sys/amd64/amd64/tsc.c
@@ -1001,7 +1001,7 @@ cpu_initclocks()
 	} else {
 		/* look for ExtInt on pin 0 */
 		if (apic_int_type(0, 0) == 3) {
-			apic_8254_intr = 0;
+			apic_8254_intr = apic_irq(0, 0);
 			setup_8254_mixed_mode();
 		} else 
 			panic("APIC_IO: Cannot route 8254 interrupt to CPU");
@@ -1062,21 +1062,39 @@ cpu_initclocks()
 			INTRDIS(1 << apic_8254_intr);
 			inthand_remove(clkdesc);
 			printf("APIC_IO: Broken MP table detected: "
-			       "8254 is not connected to IO APIC int pin %d\n",
-			       apic_8254_intr);
-			
-			apic_8254_intr = 0;
+			       "8254 is not connected to "
+			       "IOAPIC #%d intpin %d\n",
+			       int_to_apicintpin[apic_8254_intr].ioapic,
+			       int_to_apicintpin[apic_8254_intr].int_pin);
+			/* 
+			 * Revoke current ISA IRQ 0 assignment and 
+			 * configure a fallback interrupt routing from
+			 * the 8254 Timer via the 8259 PIC to the
+			 * an ExtInt interrupt line on IOAPIC #0 intpin 0.
+			 * We reuse the low level interrupt handler number.
+			 */
+			if (apic_irq(0, 0) < 0) {
+				revoke_apic_irq(apic_8254_intr);
+				assign_apic_irq(0, 0, apic_8254_intr);
+			}
+			apic_8254_intr = apic_irq(0, 0);
 			setup_8254_mixed_mode();
-			inthand_add("clk", apic_8254_intr,(inthand2_t *)clkintr,
+			inthand_add("clk", apic_8254_intr,
+				    (inthand2_t *)clkintr,
 				    NULL, &clk_imask, INTR_EXCL);
 			INTREN(1 << apic_8254_intr);
 		}
 		
 	}
-	if (apic_8254_intr)
-		printf("APIC_IO: routing 8254 via pin %d\n",apic_8254_intr);
+	if (apic_int_type(0, 0) != 3 ||
+	    int_to_apicintpin[apic_8254_intr].ioapic != 0 ||
+	    int_to_apicintpin[apic_8254_intr].int_pin != 0)
+		printf("APIC_IO: routing 8254 via IOAPIC #%d intpin %d\n",
+		       int_to_apicintpin[apic_8254_intr].ioapic,
+		       int_to_apicintpin[apic_8254_intr].int_pin);
 	else
-		printf("APIC_IO: routing 8254 via 8259 on pin 0\n");
+		printf("APIC_IO: "
+		       "routing 8254 via 8259 and IOAPIC #0 intpin 0\n");
 #endif
 	
 }
diff --git a/sys/amd64/include/mptable.h b/sys/amd64/include/mptable.h
index b565cee..48d716a 100644
--- a/sys/amd64/include/mptable.h
+++ b/sys/amd64/include/mptable.h
@@ -335,6 +335,7 @@ static void	init_locks(void);
 static int	start_all_aps(u_int boot_addr);
 static void	install_ap_tramp(u_int boot_addr);
 static int	start_ap(int logicalCpu, u_int boot_addr);
+static int	apic_int_is_bus_type(int intr, int bus_type);
 
 /*
  * Calculate usable address in base memory for AP trampoline code.
@@ -960,7 +961,7 @@ mptable_pass2(void)
 }
 
 
-static void
+void
 assign_apic_irq(int apic, int intpin, int irq)
 {
 	int x;
@@ -983,6 +984,34 @@ assign_apic_irq(int apic, int intpin, int irq)
 	}
 }
 
+void
+revoke_apic_irq(int irq)
+{
+	int x;
+	int oldapic;
+	int oldintpin;
+	
+	if (int_to_apicintpin[irq].ioapic == -1)
+		panic("assign_apic_irq: inconsistent table");
+	
+	oldapic = int_to_apicintpin[irq].ioapic;
+	oldintpin = int_to_apicintpin[irq].int_pin;
+
+	int_to_apicintpin[irq].ioapic = -1;
+	int_to_apicintpin[irq].int_pin = 0;
+	int_to_apicintpin[irq].apic_address = NULL;
+	int_to_apicintpin[irq].redirindex = 0;
+	
+	for (x = 0; x < nintrs; x++) {
+		if ((io_apic_ints[x].int_type == 0 || 
+		     io_apic_ints[x].int_type == 3) &&
+		    io_apic_ints[x].int_vector == 0xff &&
+		    io_apic_ints[x].dst_apic_id == IO_TO_ID(oldapic) &&
+		    io_apic_ints[x].dst_apic_int == oldintpin)
+			io_apic_ints[x].int_vector = 0xff;
+	}
+}
+
 /*
  * parse an Intel MP specification table
  */
@@ -1049,37 +1078,66 @@ fix_mp_table(void)
 }
 
 
+/* Assign low level interrupt handlers */
 static void
 setup_apic_irq_mapping(void)
 {
 	int	x;
 	int	int_vector;
 
-	/* Assign low level interrupt handlers */
+	/* Clear array */
 	for (x = 0; x < APIC_INTMAPSIZE; x++) {
 		int_to_apicintpin[x].ioapic = -1;
 		int_to_apicintpin[x].int_pin = 0;
 		int_to_apicintpin[x].apic_address = NULL;
 		int_to_apicintpin[x].redirindex = 0;
 	}
+
+	/* First assign ISA/EISA interrupts */
+	for (x = 0; x < nintrs; x++) {
+		int_vector = io_apic_ints[x].src_bus_irq;
+		if (int_vector < APIC_INTMAPSIZE &&
+		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
+		    (apic_int_is_bus_type(x, ISA) ||
+		     apic_int_is_bus_type(x, EISA)) &&
+		    io_apic_ints[x].int_type == 0) {
+			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id), 
+					io_apic_ints[x].dst_apic_int,
+					int_vector);
+		}
+	}
+
+	/* Assign interrupts on first 24 intpins on IOAPIC #0 */
 	for (x = 0; x < nintrs; x++) {
-		if (io_apic_ints[x].dst_apic_int < APIC_INTMAPSIZE &&
+		int_vector = io_apic_ints[x].dst_apic_int;
+		if (int_vector < APIC_INTMAPSIZE &&
 		    io_apic_ints[x].dst_apic_id == IO_TO_ID(0) &&
 		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
 		    (io_apic_ints[x].int_type == 0 ||
 		     io_apic_ints[x].int_type == 3)) {
-			assign_apic_irq(0, 
+			assign_apic_irq(0,
 					io_apic_ints[x].dst_apic_int,
-					io_apic_ints[x].dst_apic_int);
+					int_vector);
 		}
 	}
+	/* 
+	 * Assign interrupts for remaining intpins.
+	 * Skip IOAPIC #0 intpin 0 if the type is ExtInt, since this indicates
+	 * that an entry for ISA/EISA irq 0 exist, and a fallback to mixed mode
+	 * due to 8254 interrupts not being delivered can reuse that low level
+	 * interrupt handler.
+	 */
 	int_vector = 0;
 	while (int_vector < APIC_INTMAPSIZE &&
 	       int_to_apicintpin[int_vector].ioapic != -1)
 		int_vector++;
 	for (x = 0; x < nintrs && int_vector < APIC_INTMAPSIZE; x++) {
 		if ((io_apic_ints[x].int_type == 0 ||
-		     io_apic_ints[x].int_type == 3) &&
+		     (io_apic_ints[x].int_type == 3 &&
+		      (io_apic_ints[x].dst_apic_id != IO_TO_ID(0) ||
+		       io_apic_ints[x].dst_apic_int != 0))) &&
 		    io_apic_ints[x].int_vector == 0xff) {
 			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id),
 					io_apic_ints[x].dst_apic_int,
diff --git a/sys/amd64/include/smp.h b/sys/amd64/include/smp.h
index 8f0a2f8..c2340ae 100644
--- a/sys/amd64/include/smp.h
+++ b/sys/amd64/include/smp.h
@@ -132,6 +132,8 @@ int	apic_src_bus_irq	__P((int, int));
 int	apic_int_type		__P((int, int));
 int	apic_trigger		__P((int, int));
 int	apic_polarity		__P((int, int));
+void	assign_apic_irq		__P((int apic, int intpin, int irq));
+void	revoke_apic_irq		__P((int irq));
 void	bsp_apic_configure	__P((void));
 void	init_secondary		__P((void));
 void	smp_invltlb		__P((void));
diff --git a/sys/amd64/isa/clock.c b/sys/amd64/isa/clock.c
index 11b1426..ea39018 100644
--- a/sys/amd64/isa/clock.c
+++ b/sys/amd64/isa/clock.c
@@ -1001,7 +1001,7 @@ cpu_initclocks()
 	} else {
 		/* look for ExtInt on pin 0 */
 		if (apic_int_type(0, 0) == 3) {
-			apic_8254_intr = 0;
+			apic_8254_intr = apic_irq(0, 0);
 			setup_8254_mixed_mode();
 		} else 
 			panic("APIC_IO: Cannot route 8254 interrupt to CPU");
@@ -1062,21 +1062,39 @@ cpu_initclocks()
 			INTRDIS(1 << apic_8254_intr);
 			inthand_remove(clkdesc);
 			printf("APIC_IO: Broken MP table detected: "
-			       "8254 is not connected to IO APIC int pin %d\n",
-			       apic_8254_intr);
-			
-			apic_8254_intr = 0;
+			       "8254 is not connected to "
+			       "IOAPIC #%d intpin %d\n",
+			       int_to_apicintpin[apic_8254_intr].ioapic,
+			       int_to_apicintpin[apic_8254_intr].int_pin);
+			/* 
+			 * Revoke current ISA IRQ 0 assignment and 
+			 * configure a fallback interrupt routing from
+			 * the 8254 Timer via the 8259 PIC to the
+			 * an ExtInt interrupt line on IOAPIC #0 intpin 0.
+			 * We reuse the low level interrupt handler number.
+			 */
+			if (apic_irq(0, 0) < 0) {
+				revoke_apic_irq(apic_8254_intr);
+				assign_apic_irq(0, 0, apic_8254_intr);
+			}
+			apic_8254_intr = apic_irq(0, 0);
 			setup_8254_mixed_mode();
-			inthand_add("clk", apic_8254_intr,(inthand2_t *)clkintr,
+			inthand_add("clk", apic_8254_intr,
+				    (inthand2_t *)clkintr,
 				    NULL, &clk_imask, INTR_EXCL);
 			INTREN(1 << apic_8254_intr);
 		}
 		
 	}
-	if (apic_8254_intr)
-		printf("APIC_IO: routing 8254 via pin %d\n",apic_8254_intr);
+	if (apic_int_type(0, 0) != 3 ||
+	    int_to_apicintpin[apic_8254_intr].ioapic != 0 ||
+	    int_to_apicintpin[apic_8254_intr].int_pin != 0)
+		printf("APIC_IO: routing 8254 via IOAPIC #%d intpin %d\n",
+		       int_to_apicintpin[apic_8254_intr].ioapic,
+		       int_to_apicintpin[apic_8254_intr].int_pin);
 	else
-		printf("APIC_IO: routing 8254 via 8259 on pin 0\n");
+		printf("APIC_IO: "
+		       "routing 8254 via 8259 and IOAPIC #0 intpin 0\n");
 #endif
 	
 }
diff --git a/sys/i386/i386/mp_machdep.c b/sys/i386/i386/mp_machdep.c
index b565cee..48d716a 100644
--- a/sys/i386/i386/mp_machdep.c
+++ b/sys/i386/i386/mp_machdep.c
@@ -335,6 +335,7 @@ static void	init_locks(void);
 static int	start_all_aps(u_int boot_addr);
 static void	install_ap_tramp(u_int boot_addr);
 static int	start_ap(int logicalCpu, u_int boot_addr);
+static int	apic_int_is_bus_type(int intr, int bus_type);
 
 /*
  * Calculate usable address in base memory for AP trampoline code.
@@ -960,7 +961,7 @@ mptable_pass2(void)
 }
 
 
-static void
+void
 assign_apic_irq(int apic, int intpin, int irq)
 {
 	int x;
@@ -983,6 +984,34 @@ assign_apic_irq(int apic, int intpin, int irq)
 	}
 }
 
+void
+revoke_apic_irq(int irq)
+{
+	int x;
+	int oldapic;
+	int oldintpin;
+	
+	if (int_to_apicintpin[irq].ioapic == -1)
+		panic("assign_apic_irq: inconsistent table");
+	
+	oldapic = int_to_apicintpin[irq].ioapic;
+	oldintpin = int_to_apicintpin[irq].int_pin;
+
+	int_to_apicintpin[irq].ioapic = -1;
+	int_to_apicintpin[irq].int_pin = 0;
+	int_to_apicintpin[irq].apic_address = NULL;
+	int_to_apicintpin[irq].redirindex = 0;
+	
+	for (x = 0; x < nintrs; x++) {
+		if ((io_apic_ints[x].int_type == 0 || 
+		     io_apic_ints[x].int_type == 3) &&
+		    io_apic_ints[x].int_vector == 0xff &&
+		    io_apic_ints[x].dst_apic_id == IO_TO_ID(oldapic) &&
+		    io_apic_ints[x].dst_apic_int == oldintpin)
+			io_apic_ints[x].int_vector = 0xff;
+	}
+}
+
 /*
  * parse an Intel MP specification table
  */
@@ -1049,37 +1078,66 @@ fix_mp_table(void)
 }
 
 
+/* Assign low level interrupt handlers */
 static void
 setup_apic_irq_mapping(void)
 {
 	int	x;
 	int	int_vector;
 
-	/* Assign low level interrupt handlers */
+	/* Clear array */
 	for (x = 0; x < APIC_INTMAPSIZE; x++) {
 		int_to_apicintpin[x].ioapic = -1;
 		int_to_apicintpin[x].int_pin = 0;
 		int_to_apicintpin[x].apic_address = NULL;
 		int_to_apicintpin[x].redirindex = 0;
 	}
+
+	/* First assign ISA/EISA interrupts */
+	for (x = 0; x < nintrs; x++) {
+		int_vector = io_apic_ints[x].src_bus_irq;
+		if (int_vector < APIC_INTMAPSIZE &&
+		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
+		    (apic_int_is_bus_type(x, ISA) ||
+		     apic_int_is_bus_type(x, EISA)) &&
+		    io_apic_ints[x].int_type == 0) {
+			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id), 
+					io_apic_ints[x].dst_apic_int,
+					int_vector);
+		}
+	}
+
+	/* Assign interrupts on first 24 intpins on IOAPIC #0 */
 	for (x = 0; x < nintrs; x++) {
-		if (io_apic_ints[x].dst_apic_int < APIC_INTMAPSIZE &&
+		int_vector = io_apic_ints[x].dst_apic_int;
+		if (int_vector < APIC_INTMAPSIZE &&
 		    io_apic_ints[x].dst_apic_id == IO_TO_ID(0) &&
 		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
 		    (io_apic_ints[x].int_type == 0 ||
 		     io_apic_ints[x].int_type == 3)) {
-			assign_apic_irq(0, 
+			assign_apic_irq(0,
 					io_apic_ints[x].dst_apic_int,
-					io_apic_ints[x].dst_apic_int);
+					int_vector);
 		}
 	}
+	/* 
+	 * Assign interrupts for remaining intpins.
+	 * Skip IOAPIC #0 intpin 0 if the type is ExtInt, since this indicates
+	 * that an entry for ISA/EISA irq 0 exist, and a fallback to mixed mode
+	 * due to 8254 interrupts not being delivered can reuse that low level
+	 * interrupt handler.
+	 */
 	int_vector = 0;
 	while (int_vector < APIC_INTMAPSIZE &&
 	       int_to_apicintpin[int_vector].ioapic != -1)
 		int_vector++;
 	for (x = 0; x < nintrs && int_vector < APIC_INTMAPSIZE; x++) {
 		if ((io_apic_ints[x].int_type == 0 ||
-		     io_apic_ints[x].int_type == 3) &&
+		     (io_apic_ints[x].int_type == 3 &&
+		      (io_apic_ints[x].dst_apic_id != IO_TO_ID(0) ||
+		       io_apic_ints[x].dst_apic_int != 0))) &&
 		    io_apic_ints[x].int_vector == 0xff) {
 			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id),
 					io_apic_ints[x].dst_apic_int,
diff --git a/sys/i386/i386/mptable.c b/sys/i386/i386/mptable.c
index b565cee..48d716a 100644
--- a/sys/i386/i386/mptable.c
+++ b/sys/i386/i386/mptable.c
@@ -335,6 +335,7 @@ static void	init_locks(void);
 static int	start_all_aps(u_int boot_addr);
 static void	install_ap_tramp(u_int boot_addr);
 static int	start_ap(int logicalCpu, u_int boot_addr);
+static int	apic_int_is_bus_type(int intr, int bus_type);
 
 /*
  * Calculate usable address in base memory for AP trampoline code.
@@ -960,7 +961,7 @@ mptable_pass2(void)
 }
 
 
-static void
+void
 assign_apic_irq(int apic, int intpin, int irq)
 {
 	int x;
@@ -983,6 +984,34 @@ assign_apic_irq(int apic, int intpin, int irq)
 	}
 }
 
+void
+revoke_apic_irq(int irq)
+{
+	int x;
+	int oldapic;
+	int oldintpin;
+	
+	if (int_to_apicintpin[irq].ioapic == -1)
+		panic("assign_apic_irq: inconsistent table");
+	
+	oldapic = int_to_apicintpin[irq].ioapic;
+	oldintpin = int_to_apicintpin[irq].int_pin;
+
+	int_to_apicintpin[irq].ioapic = -1;
+	int_to_apicintpin[irq].int_pin = 0;
+	int_to_apicintpin[irq].apic_address = NULL;
+	int_to_apicintpin[irq].redirindex = 0;
+	
+	for (x = 0; x < nintrs; x++) {
+		if ((io_apic_ints[x].int_type == 0 || 
+		     io_apic_ints[x].int_type == 3) &&
+		    io_apic_ints[x].int_vector == 0xff &&
+		    io_apic_ints[x].dst_apic_id == IO_TO_ID(oldapic) &&
+		    io_apic_ints[x].dst_apic_int == oldintpin)
+			io_apic_ints[x].int_vector = 0xff;
+	}
+}
+
 /*
  * parse an Intel MP specification table
  */
@@ -1049,37 +1078,66 @@ fix_mp_table(void)
 }
 
 
+/* Assign low level interrupt handlers */
 static void
 setup_apic_irq_mapping(void)
 {
 	int	x;
 	int	int_vector;
 
-	/* Assign low level interrupt handlers */
+	/* Clear array */
 	for (x = 0; x < APIC_INTMAPSIZE; x++) {
 		int_to_apicintpin[x].ioapic = -1;
 		int_to_apicintpin[x].int_pin = 0;
 		int_to_apicintpin[x].apic_address = NULL;
 		int_to_apicintpin[x].redirindex = 0;
 	}
+
+	/* First assign ISA/EISA interrupts */
+	for (x = 0; x < nintrs; x++) {
+		int_vector = io_apic_ints[x].src_bus_irq;
+		if (int_vector < APIC_INTMAPSIZE &&
+		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
+		    (apic_int_is_bus_type(x, ISA) ||
+		     apic_int_is_bus_type(x, EISA)) &&
+		    io_apic_ints[x].int_type == 0) {
+			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id), 
+					io_apic_ints[x].dst_apic_int,
+					int_vector);
+		}
+	}
+
+	/* Assign interrupts on first 24 intpins on IOAPIC #0 */
 	for (x = 0; x < nintrs; x++) {
-		if (io_apic_ints[x].dst_apic_int < APIC_INTMAPSIZE &&
+		int_vector = io_apic_ints[x].dst_apic_int;
+		if (int_vector < APIC_INTMAPSIZE &&
 		    io_apic_ints[x].dst_apic_id == IO_TO_ID(0) &&
 		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
 		    (io_apic_ints[x].int_type == 0 ||
 		     io_apic_ints[x].int_type == 3)) {
-			assign_apic_irq(0, 
+			assign_apic_irq(0,
 					io_apic_ints[x].dst_apic_int,
-					io_apic_ints[x].dst_apic_int);
+					int_vector);
 		}
 	}
+	/* 
+	 * Assign interrupts for remaining intpins.
+	 * Skip IOAPIC #0 intpin 0 if the type is ExtInt, since this indicates
+	 * that an entry for ISA/EISA irq 0 exist, and a fallback to mixed mode
+	 * due to 8254 interrupts not being delivered can reuse that low level
+	 * interrupt handler.
+	 */
 	int_vector = 0;
 	while (int_vector < APIC_INTMAPSIZE &&
 	       int_to_apicintpin[int_vector].ioapic != -1)
 		int_vector++;
 	for (x = 0; x < nintrs && int_vector < APIC_INTMAPSIZE; x++) {
 		if ((io_apic_ints[x].int_type == 0 ||
-		     io_apic_ints[x].int_type == 3) &&
+		     (io_apic_ints[x].int_type == 3 &&
+		      (io_apic_ints[x].dst_apic_id != IO_TO_ID(0) ||
+		       io_apic_ints[x].dst_apic_int != 0))) &&
 		    io_apic_ints[x].int_vector == 0xff) {
 			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id),
 					io_apic_ints[x].dst_apic_int,
diff --git a/sys/i386/i386/tsc.c b/sys/i386/i386/tsc.c
index 11b1426..ea39018 100644
--- a/sys/i386/i386/tsc.c
+++ b/sys/i386/i386/tsc.c
@@ -1001,7 +1001,7 @@ cpu_initclocks()
 	} else {
 		/* look for ExtInt on pin 0 */
 		if (apic_int_type(0, 0) == 3) {
-			apic_8254_intr = 0;
+			apic_8254_intr = apic_irq(0, 0);
 			setup_8254_mixed_mode();
 		} else 
 			panic("APIC_IO: Cannot route 8254 interrupt to CPU");
@@ -1062,21 +1062,39 @@ cpu_initclocks()
 			INTRDIS(1 << apic_8254_intr);
 			inthand_remove(clkdesc);
 			printf("APIC_IO: Broken MP table detected: "
-			       "8254 is not connected to IO APIC int pin %d\n",
-			       apic_8254_intr);
-			
-			apic_8254_intr = 0;
+			       "8254 is not connected to "
+			       "IOAPIC #%d intpin %d\n",
+			       int_to_apicintpin[apic_8254_intr].ioapic,
+			       int_to_apicintpin[apic_8254_intr].int_pin);
+			/* 
+			 * Revoke current ISA IRQ 0 assignment and 
+			 * configure a fallback interrupt routing from
+			 * the 8254 Timer via the 8259 PIC to the
+			 * an ExtInt interrupt line on IOAPIC #0 intpin 0.
+			 * We reuse the low level interrupt handler number.
+			 */
+			if (apic_irq(0, 0) < 0) {
+				revoke_apic_irq(apic_8254_intr);
+				assign_apic_irq(0, 0, apic_8254_intr);
+			}
+			apic_8254_intr = apic_irq(0, 0);
 			setup_8254_mixed_mode();
-			inthand_add("clk", apic_8254_intr,(inthand2_t *)clkintr,
+			inthand_add("clk", apic_8254_intr,
+				    (inthand2_t *)clkintr,
 				    NULL, &clk_imask, INTR_EXCL);
 			INTREN(1 << apic_8254_intr);
 		}
 		
 	}
-	if (apic_8254_intr)
-		printf("APIC_IO: routing 8254 via pin %d\n",apic_8254_intr);
+	if (apic_int_type(0, 0) != 3 ||
+	    int_to_apicintpin[apic_8254_intr].ioapic != 0 ||
+	    int_to_apicintpin[apic_8254_intr].int_pin != 0)
+		printf("APIC_IO: routing 8254 via IOAPIC #%d intpin %d\n",
+		       int_to_apicintpin[apic_8254_intr].ioapic,
+		       int_to_apicintpin[apic_8254_intr].int_pin);
 	else
-		printf("APIC_IO: routing 8254 via 8259 on pin 0\n");
+		printf("APIC_IO: "
+		       "routing 8254 via 8259 and IOAPIC #0 intpin 0\n");
 #endif
 	
 }
diff --git a/sys/i386/include/mptable.h b/sys/i386/include/mptable.h
index b565cee..48d716a 100644
--- a/sys/i386/include/mptable.h
+++ b/sys/i386/include/mptable.h
@@ -335,6 +335,7 @@ static void	init_locks(void);
 static int	start_all_aps(u_int boot_addr);
 static void	install_ap_tramp(u_int boot_addr);
 static int	start_ap(int logicalCpu, u_int boot_addr);
+static int	apic_int_is_bus_type(int intr, int bus_type);
 
 /*
  * Calculate usable address in base memory for AP trampoline code.
@@ -960,7 +961,7 @@ mptable_pass2(void)
 }
 
 
-static void
+void
 assign_apic_irq(int apic, int intpin, int irq)
 {
 	int x;
@@ -983,6 +984,34 @@ assign_apic_irq(int apic, int intpin, int irq)
 	}
 }
 
+void
+revoke_apic_irq(int irq)
+{
+	int x;
+	int oldapic;
+	int oldintpin;
+	
+	if (int_to_apicintpin[irq].ioapic == -1)
+		panic("assign_apic_irq: inconsistent table");
+	
+	oldapic = int_to_apicintpin[irq].ioapic;
+	oldintpin = int_to_apicintpin[irq].int_pin;
+
+	int_to_apicintpin[irq].ioapic = -1;
+	int_to_apicintpin[irq].int_pin = 0;
+	int_to_apicintpin[irq].apic_address = NULL;
+	int_to_apicintpin[irq].redirindex = 0;
+	
+	for (x = 0; x < nintrs; x++) {
+		if ((io_apic_ints[x].int_type == 0 || 
+		     io_apic_ints[x].int_type == 3) &&
+		    io_apic_ints[x].int_vector == 0xff &&
+		    io_apic_ints[x].dst_apic_id == IO_TO_ID(oldapic) &&
+		    io_apic_ints[x].dst_apic_int == oldintpin)
+			io_apic_ints[x].int_vector = 0xff;
+	}
+}
+
 /*
  * parse an Intel MP specification table
  */
@@ -1049,37 +1078,66 @@ fix_mp_table(void)
 }
 
 
+/* Assign low level interrupt handlers */
 static void
 setup_apic_irq_mapping(void)
 {
 	int	x;
 	int	int_vector;
 
-	/* Assign low level interrupt handlers */
+	/* Clear array */
 	for (x = 0; x < APIC_INTMAPSIZE; x++) {
 		int_to_apicintpin[x].ioapic = -1;
 		int_to_apicintpin[x].int_pin = 0;
 		int_to_apicintpin[x].apic_address = NULL;
 		int_to_apicintpin[x].redirindex = 0;
 	}
+
+	/* First assign ISA/EISA interrupts */
+	for (x = 0; x < nintrs; x++) {
+		int_vector = io_apic_ints[x].src_bus_irq;
+		if (int_vector < APIC_INTMAPSIZE &&
+		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
+		    (apic_int_is_bus_type(x, ISA) ||
+		     apic_int_is_bus_type(x, EISA)) &&
+		    io_apic_ints[x].int_type == 0) {
+			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id), 
+					io_apic_ints[x].dst_apic_int,
+					int_vector);
+		}
+	}
+
+	/* Assign interrupts on first 24 intpins on IOAPIC #0 */
 	for (x = 0; x < nintrs; x++) {
-		if (io_apic_ints[x].dst_apic_int < APIC_INTMAPSIZE &&
+		int_vector = io_apic_ints[x].dst_apic_int;
+		if (int_vector < APIC_INTMAPSIZE &&
 		    io_apic_ints[x].dst_apic_id == IO_TO_ID(0) &&
 		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
 		    (io_apic_ints[x].int_type == 0 ||
 		     io_apic_ints[x].int_type == 3)) {
-			assign_apic_irq(0, 
+			assign_apic_irq(0,
 					io_apic_ints[x].dst_apic_int,
-					io_apic_ints[x].dst_apic_int);
+					int_vector);
 		}
 	}
+	/* 
+	 * Assign interrupts for remaining intpins.
+	 * Skip IOAPIC #0 intpin 0 if the type is ExtInt, since this indicates
+	 * that an entry for ISA/EISA irq 0 exist, and a fallback to mixed mode
+	 * due to 8254 interrupts not being delivered can reuse that low level
+	 * interrupt handler.
+	 */
 	int_vector = 0;
 	while (int_vector < APIC_INTMAPSIZE &&
 	       int_to_apicintpin[int_vector].ioapic != -1)
 		int_vector++;
 	for (x = 0; x < nintrs && int_vector < APIC_INTMAPSIZE; x++) {
 		if ((io_apic_ints[x].int_type == 0 ||
-		     io_apic_ints[x].int_type == 3) &&
+		     (io_apic_ints[x].int_type == 3 &&
+		      (io_apic_ints[x].dst_apic_id != IO_TO_ID(0) ||
+		       io_apic_ints[x].dst_apic_int != 0))) &&
 		    io_apic_ints[x].int_vector == 0xff) {
 			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id),
 					io_apic_ints[x].dst_apic_int,
diff --git a/sys/i386/include/smp.h b/sys/i386/include/smp.h
index 8f0a2f8..c2340ae 100644
--- a/sys/i386/include/smp.h
+++ b/sys/i386/include/smp.h
@@ -132,6 +132,8 @@ int	apic_src_bus_irq	__P((int, int));
 int	apic_int_type		__P((int, int));
 int	apic_trigger		__P((int, int));
 int	apic_polarity		__P((int, int));
+void	assign_apic_irq		__P((int apic, int intpin, int irq));
+void	revoke_apic_irq		__P((int irq));
 void	bsp_apic_configure	__P((void));
 void	init_secondary		__P((void));
 void	smp_invltlb		__P((void));
diff --git a/sys/i386/isa/clock.c b/sys/i386/isa/clock.c
index 11b1426..ea39018 100644
--- a/sys/i386/isa/clock.c
+++ b/sys/i386/isa/clock.c
@@ -1001,7 +1001,7 @@ cpu_initclocks()
 	} else {
 		/* look for ExtInt on pin 0 */
 		if (apic_int_type(0, 0) == 3) {
-			apic_8254_intr = 0;
+			apic_8254_intr = apic_irq(0, 0);
 			setup_8254_mixed_mode();
 		} else 
 			panic("APIC_IO: Cannot route 8254 interrupt to CPU");
@@ -1062,21 +1062,39 @@ cpu_initclocks()
 			INTRDIS(1 << apic_8254_intr);
 			inthand_remove(clkdesc);
 			printf("APIC_IO: Broken MP table detected: "
-			       "8254 is not connected to IO APIC int pin %d\n",
-			       apic_8254_intr);
-			
-			apic_8254_intr = 0;
+			       "8254 is not connected to "
+			       "IOAPIC #%d intpin %d\n",
+			       int_to_apicintpin[apic_8254_intr].ioapic,
+			       int_to_apicintpin[apic_8254_intr].int_pin);
+			/* 
+			 * Revoke current ISA IRQ 0 assignment and 
+			 * configure a fallback interrupt routing from
+			 * the 8254 Timer via the 8259 PIC to the
+			 * an ExtInt interrupt line on IOAPIC #0 intpin 0.
+			 * We reuse the low level interrupt handler number.
+			 */
+			if (apic_irq(0, 0) < 0) {
+				revoke_apic_irq(apic_8254_intr);
+				assign_apic_irq(0, 0, apic_8254_intr);
+			}
+			apic_8254_intr = apic_irq(0, 0);
 			setup_8254_mixed_mode();
-			inthand_add("clk", apic_8254_intr,(inthand2_t *)clkintr,
+			inthand_add("clk", apic_8254_intr,
+				    (inthand2_t *)clkintr,
 				    NULL, &clk_imask, INTR_EXCL);
 			INTREN(1 << apic_8254_intr);
 		}
 		
 	}
-	if (apic_8254_intr)
-		printf("APIC_IO: routing 8254 via pin %d\n",apic_8254_intr);
+	if (apic_int_type(0, 0) != 3 ||
+	    int_to_apicintpin[apic_8254_intr].ioapic != 0 ||
+	    int_to_apicintpin[apic_8254_intr].int_pin != 0)
+		printf("APIC_IO: routing 8254 via IOAPIC #%d intpin %d\n",
+		       int_to_apicintpin[apic_8254_intr].ioapic,
+		       int_to_apicintpin[apic_8254_intr].int_pin);
 	else
-		printf("APIC_IO: routing 8254 via 8259 on pin 0\n");
+		printf("APIC_IO: "
+		       "routing 8254 via 8259 and IOAPIC #0 intpin 0\n");
 #endif
 	
 }
diff --git a/sys/isa/atrtc.c b/sys/isa/atrtc.c
index 11b1426..ea39018 100644
--- a/sys/isa/atrtc.c
+++ b/sys/isa/atrtc.c
@@ -1001,7 +1001,7 @@ cpu_initclocks()
 	} else {
 		/* look for ExtInt on pin 0 */
 		if (apic_int_type(0, 0) == 3) {
-			apic_8254_intr = 0;
+			apic_8254_intr = apic_irq(0, 0);
 			setup_8254_mixed_mode();
 		} else 
 			panic("APIC_IO: Cannot route 8254 interrupt to CPU");
@@ -1062,21 +1062,39 @@ cpu_initclocks()
 			INTRDIS(1 << apic_8254_intr);
 			inthand_remove(clkdesc);
 			printf("APIC_IO: Broken MP table detected: "
-			       "8254 is not connected to IO APIC int pin %d\n",
-			       apic_8254_intr);
-			
-			apic_8254_intr = 0;
+			       "8254 is not connected to "
+			       "IOAPIC #%d intpin %d\n",
+			       int_to_apicintpin[apic_8254_intr].ioapic,
+			       int_to_apicintpin[apic_8254_intr].int_pin);
+			/* 
+			 * Revoke current ISA IRQ 0 assignment and 
+			 * configure a fallback interrupt routing from
+			 * the 8254 Timer via the 8259 PIC to the
+			 * an ExtInt interrupt line on IOAPIC #0 intpin 0.
+			 * We reuse the low level interrupt handler number.
+			 */
+			if (apic_irq(0, 0) < 0) {
+				revoke_apic_irq(apic_8254_intr);
+				assign_apic_irq(0, 0, apic_8254_intr);
+			}
+			apic_8254_intr = apic_irq(0, 0);
 			setup_8254_mixed_mode();
-			inthand_add("clk", apic_8254_intr,(inthand2_t *)clkintr,
+			inthand_add("clk", apic_8254_intr,
+				    (inthand2_t *)clkintr,
 				    NULL, &clk_imask, INTR_EXCL);
 			INTREN(1 << apic_8254_intr);
 		}
 		
 	}
-	if (apic_8254_intr)
-		printf("APIC_IO: routing 8254 via pin %d\n",apic_8254_intr);
+	if (apic_int_type(0, 0) != 3 ||
+	    int_to_apicintpin[apic_8254_intr].ioapic != 0 ||
+	    int_to_apicintpin[apic_8254_intr].int_pin != 0)
+		printf("APIC_IO: routing 8254 via IOAPIC #%d intpin %d\n",
+		       int_to_apicintpin[apic_8254_intr].ioapic,
+		       int_to_apicintpin[apic_8254_intr].int_pin);
 	else
-		printf("APIC_IO: routing 8254 via 8259 on pin 0\n");
+		printf("APIC_IO: "
+		       "routing 8254 via 8259 and IOAPIC #0 intpin 0\n");
 #endif
 	
 }
diff --git a/sys/kern/subr_smp.c b/sys/kern/subr_smp.c
index b565cee..48d716a 100644
--- a/sys/kern/subr_smp.c
+++ b/sys/kern/subr_smp.c
@@ -335,6 +335,7 @@ static void	init_locks(void);
 static int	start_all_aps(u_int boot_addr);
 static void	install_ap_tramp(u_int boot_addr);
 static int	start_ap(int logicalCpu, u_int boot_addr);
+static int	apic_int_is_bus_type(int intr, int bus_type);
 
 /*
  * Calculate usable address in base memory for AP trampoline code.
@@ -960,7 +961,7 @@ mptable_pass2(void)
 }
 
 
-static void
+void
 assign_apic_irq(int apic, int intpin, int irq)
 {
 	int x;
@@ -983,6 +984,34 @@ assign_apic_irq(int apic, int intpin, int irq)
 	}
 }
 
+void
+revoke_apic_irq(int irq)
+{
+	int x;
+	int oldapic;
+	int oldintpin;
+	
+	if (int_to_apicintpin[irq].ioapic == -1)
+		panic("assign_apic_irq: inconsistent table");
+	
+	oldapic = int_to_apicintpin[irq].ioapic;
+	oldintpin = int_to_apicintpin[irq].int_pin;
+
+	int_to_apicintpin[irq].ioapic = -1;
+	int_to_apicintpin[irq].int_pin = 0;
+	int_to_apicintpin[irq].apic_address = NULL;
+	int_to_apicintpin[irq].redirindex = 0;
+	
+	for (x = 0; x < nintrs; x++) {
+		if ((io_apic_ints[x].int_type == 0 || 
+		     io_apic_ints[x].int_type == 3) &&
+		    io_apic_ints[x].int_vector == 0xff &&
+		    io_apic_ints[x].dst_apic_id == IO_TO_ID(oldapic) &&
+		    io_apic_ints[x].dst_apic_int == oldintpin)
+			io_apic_ints[x].int_vector = 0xff;
+	}
+}
+
 /*
  * parse an Intel MP specification table
  */
@@ -1049,37 +1078,66 @@ fix_mp_table(void)
 }
 
 
+/* Assign low level interrupt handlers */
 static void
 setup_apic_irq_mapping(void)
 {
 	int	x;
 	int	int_vector;
 
-	/* Assign low level interrupt handlers */
+	/* Clear array */
 	for (x = 0; x < APIC_INTMAPSIZE; x++) {
 		int_to_apicintpin[x].ioapic = -1;
 		int_to_apicintpin[x].int_pin = 0;
 		int_to_apicintpin[x].apic_address = NULL;
 		int_to_apicintpin[x].redirindex = 0;
 	}
+
+	/* First assign ISA/EISA interrupts */
+	for (x = 0; x < nintrs; x++) {
+		int_vector = io_apic_ints[x].src_bus_irq;
+		if (int_vector < APIC_INTMAPSIZE &&
+		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
+		    (apic_int_is_bus_type(x, ISA) ||
+		     apic_int_is_bus_type(x, EISA)) &&
+		    io_apic_ints[x].int_type == 0) {
+			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id), 
+					io_apic_ints[x].dst_apic_int,
+					int_vector);
+		}
+	}
+
+	/* Assign interrupts on first 24 intpins on IOAPIC #0 */
 	for (x = 0; x < nintrs; x++) {
-		if (io_apic_ints[x].dst_apic_int < APIC_INTMAPSIZE &&
+		int_vector = io_apic_ints[x].dst_apic_int;
+		if (int_vector < APIC_INTMAPSIZE &&
 		    io_apic_ints[x].dst_apic_id == IO_TO_ID(0) &&
 		    io_apic_ints[x].int_vector == 0xff && 
+		    int_to_apicintpin[int_vector].ioapic == -1 &&
 		    (io_apic_ints[x].int_type == 0 ||
 		     io_apic_ints[x].int_type == 3)) {
-			assign_apic_irq(0, 
+			assign_apic_irq(0,
 					io_apic_ints[x].dst_apic_int,
-					io_apic_ints[x].dst_apic_int);
+					int_vector);
 		}
 	}
+	/* 
+	 * Assign interrupts for remaining intpins.
+	 * Skip IOAPIC #0 intpin 0 if the type is ExtInt, since this indicates
+	 * that an entry for ISA/EISA irq 0 exist, and a fallback to mixed mode
+	 * due to 8254 interrupts not being delivered can reuse that low level
+	 * interrupt handler.
+	 */
 	int_vector = 0;
 	while (int_vector < APIC_INTMAPSIZE &&
 	       int_to_apicintpin[int_vector].ioapic != -1)
 		int_vector++;
 	for (x = 0; x < nintrs && int_vector < APIC_INTMAPSIZE; x++) {
 		if ((io_apic_ints[x].int_type == 0 ||
-		     io_apic_ints[x].int_type == 3) &&
+		     (io_apic_ints[x].int_type == 3 &&
+		      (io_apic_ints[x].dst_apic_id != IO_TO_ID(0) ||
+		       io_apic_ints[x].dst_apic_int != 0))) &&
 		    io_apic_ints[x].int_vector == 0xff) {
 			assign_apic_irq(ID_TO_IO(io_apic_ints[x].dst_apic_id),
 					io_apic_ints[x].dst_apic_int,
diff --git a/sys/sys/smp.h b/sys/sys/smp.h
index 8f0a2f8..c2340ae 100644
--- a/sys/sys/smp.h
+++ b/sys/sys/smp.h
@@ -132,6 +132,8 @@ int	apic_src_bus_irq	__P((int, int));
 int	apic_int_type		__P((int, int));
 int	apic_trigger		__P((int, int));
 int	apic_polarity		__P((int, int));
+void	assign_apic_irq		__P((int apic, int intpin, int irq));
+void	revoke_apic_irq		__P((int irq));
 void	bsp_apic_configure	__P((void));
 void	init_secondary		__P((void));
 void	smp_invltlb		__P((void));