diff --git a/arch/m68k/include/asm/mac_oss.h b/arch/m68k/include/asm/mac_oss.h
index 3f04a66..425fbff 100644
--- a/arch/m68k/include/asm/mac_oss.h
+++ b/arch/m68k/include/asm/mac_oss.h
@@ -58,25 +58,6 @@
 
 #define OSS_POWEROFF	0x80
 
-/*
- * OSS Interrupt levels for various sub-systems
- *
- * This mapping is laid out with two things in mind: first, we try to keep
- * things on their own levels to avoid having to do double-dispatches. Second,
- * the levels match as closely as possible the alternate IRQ mapping mode (aka
- * "A/UX mode") available on some VIA machines.
- */
-
-#define OSS_IRQLEV_DISABLED	0
-#define OSS_IRQLEV_IOPISM	1	/* ADB? */
-#define OSS_IRQLEV_SCSI		IRQ_AUTO_2
-#define OSS_IRQLEV_NUBUS	IRQ_AUTO_3	/* keep this on its own level */
-#define OSS_IRQLEV_IOPSCC	IRQ_AUTO_4	/* matches VIA alternate mapping */
-#define OSS_IRQLEV_SOUND	IRQ_AUTO_5	/* matches VIA alternate mapping */
-#define OSS_IRQLEV_60HZ		6	/* matches VIA alternate mapping */
-#define OSS_IRQLEV_VIA1		IRQ_AUTO_6	/* matches VIA alternate mapping */
-#define OSS_IRQLEV_PARITY	7	/* matches VIA alternate mapping */
-
 #ifndef __ASSEMBLY__
 
 struct mac_oss {
diff --git a/arch/m68k/include/asm/macints.h b/arch/m68k/include/asm/macints.h
index ebe1b70..92aa8a4 100644
--- a/arch/m68k/include/asm/macints.h
+++ b/arch/m68k/include/asm/macints.h
@@ -104,6 +104,9 @@
 #define IRQ_PSC4_3	  (35)
 #define IRQ_MAC_MACE_DMA  IRQ_PSC4_3
 
+/* OSS Level 4 interrupts */
+#define IRQ_MAC_SCC	  (33)
+
 /* Level 5 (PSC, AV Macs only) interrupts */
 #define IRQ_PSC5_0	  (40)
 #define IRQ_PSC5_1	  (41)
@@ -131,9 +134,6 @@
 #define IRQ_BABOON_2	  (66)
 #define IRQ_BABOON_3	  (67)
 
-/* On non-PSC machines, the serial ports share an IRQ */
-#define IRQ_MAC_SCC	  IRQ_AUTO_4
-
 #define SLOT2IRQ(x)	  (x + 47)
 #define IRQ2SLOT(x)	  (x - 47)
 
diff --git a/arch/m68k/mac/config.c b/arch/m68k/mac/config.c
index 12e564c..101a8b7 100644
--- a/arch/m68k/mac/config.c
+++ b/arch/m68k/mac/config.c
@@ -893,8 +893,14 @@
 		scc_b_rsrcs[1].start = scc_b_rsrcs[1].end = IRQ_MAC_SCC_B;
 		break;
 	default:
-		scc_a_rsrcs[1].start = scc_a_rsrcs[1].end = IRQ_MAC_SCC;
-		scc_b_rsrcs[1].start = scc_b_rsrcs[1].end = IRQ_MAC_SCC;
+		/* On non-PSC machines, the serial ports share an IRQ. */
+		if (macintosh_config->ident == MAC_MODEL_IIFX) {
+			scc_a_rsrcs[1].start = scc_a_rsrcs[1].end = IRQ_MAC_SCC;
+			scc_b_rsrcs[1].start = scc_b_rsrcs[1].end = IRQ_MAC_SCC;
+		} else {
+			scc_a_rsrcs[1].start = scc_a_rsrcs[1].end = IRQ_AUTO_4;
+			scc_b_rsrcs[1].start = scc_b_rsrcs[1].end = IRQ_AUTO_4;
+		}
 		break;
 	}
 
diff --git a/arch/m68k/mac/iop.c b/arch/m68k/mac/iop.c
index a5462cc..7d8d461 100644
--- a/arch/m68k/mac/iop.c
+++ b/arch/m68k/mac/iop.c
@@ -115,7 +115,6 @@
 #include <asm/macintosh.h>
 #include <asm/macints.h>
 #include <asm/mac_iop.h>
-#include <asm/mac_oss.h>
 
 /*#define DEBUG_IOP*/
 
@@ -149,8 +148,6 @@
 
 irqreturn_t iop_ism_irq(int, void *);
 
-extern void oss_irq_enable(int);
-
 /*
  * Private access functions
  */
@@ -304,11 +301,10 @@
 void __init iop_register_interrupts(void)
 {
 	if (iop_ism_present) {
-		if (oss_present) {
-			if (request_irq(OSS_IRQLEV_IOPISM, iop_ism_irq, 0,
+		if (macintosh_config->ident == MAC_MODEL_IIFX) {
+			if (request_irq(IRQ_MAC_ADB, iop_ism_irq, 0,
 					"ISM IOP", (void *)IOP_NUM_ISM))
 				pr_err("Couldn't register ISM IOP interrupt\n");
-			oss_irq_enable(IRQ_MAC_ADB);
 		} else {
 			if (request_irq(IRQ_VIA2_0, iop_ism_irq, 0, "ISM IOP",
 					(void *)IOP_NUM_ISM))
diff --git a/arch/m68k/mac/macints.c b/arch/m68k/mac/macints.c
index 74f5a97..5c1a6b2 100644
--- a/arch/m68k/mac/macints.c
+++ b/arch/m68k/mac/macints.c
@@ -26,10 +26,6 @@
  *		  - slot 6: timer 1 (not on IIci)
  *		  - slot 7: status of IRQ; signals 'any enabled int.'
  *
- *	2	- OSS (IIfx only?)
- *		  - slot 0: SCSI interrupt
- *		  - slot 1: Sound interrupt
- *
  * Levels 3-6 vary by machine type. For VIA or RBV Macintoshes:
  *
  *	3	- unused (?)
@@ -54,21 +50,18 @@
  *
  *	6	- VIA1
  *
- * For OSS Macintoshes (IIfx only at this point):
+ * For OSS Macintoshes (IIfx only), we apply an interrupt mapping similar to
+ * the Quadra (A/UX) mapping:
  *
- *	3	- Nubus interrupt
- *		  - slot 0: Slot $9
- *		  - slot 1: Slot $A
- *		  - slot 2: Slot $B
- *		  - slot 3: Slot $C
- *		  - slot 4: Slot $D
- *		  - slot 5: Slot $E
+ *	1	- ISM IOP (ADB)
+ *
+ *	2	- SCSI
+ *
+ *	3	- NuBus
  *
  *	4	- SCC IOP
  *
- *	5	- ISM IOP (ADB?)
- *
- *	6	- unused
+ *	6	- VIA1
  *
  * For PSC Macintoshes (660AV, 840AV):
  *
@@ -112,14 +105,6 @@
  *   case. They're hidden behind the Nubus slot $C interrupt thus adding a
  *   third layer of indirection. Why oh why did the Apple engineers do that?
  *
- * - We support "fast" and "slow" handlers, just like the Amiga port. The
- *   fast handlers are called first and with all interrupts disabled. They
- *   are expected to execute quickly (hence the name). The slow handlers are
- *   called last with interrupts enabled and the interrupt level restored.
- *   They must therefore be reentrant.
- *
- *   TODO:
- *
  */
 
 #include <linux/types.h>
@@ -216,8 +201,6 @@
 
 	switch(irq_src) {
 	case 1:
-		via_irq_enable(irq);
-		break;
 	case 2:
 	case 7:
 		if (oss_present)
@@ -226,6 +209,7 @@
 			via_irq_enable(irq);
 		break;
 	case 3:
+	case 4:
 	case 5:
 	case 6:
 		if (psc_present)
@@ -233,10 +217,6 @@
 		else if (oss_present)
 			oss_irq_enable(irq);
 		break;
-	case 4:
-		if (psc_present)
-			psc_irq_enable(irq);
-		break;
 	case 8:
 		if (baboon_present)
 			baboon_irq_enable(irq);
@@ -251,8 +231,6 @@
 
 	switch(irq_src) {
 	case 1:
-		via_irq_disable(irq);
-		break;
 	case 2:
 	case 7:
 		if (oss_present)
@@ -261,6 +239,7 @@
 			via_irq_disable(irq);
 		break;
 	case 3:
+	case 4:
 	case 5:
 	case 6:
 		if (psc_present)
@@ -268,10 +247,6 @@
 		else if (oss_present)
 			oss_irq_disable(irq);
 		break;
-	case 4:
-		if (psc_present)
-			psc_irq_disable(irq);
-		break;
 	case 8:
 		if (baboon_present)
 			baboon_irq_disable(irq);
diff --git a/arch/m68k/mac/oss.c b/arch/m68k/mac/oss.c
index fdc0f84..6c4c882 100644
--- a/arch/m68k/mac/oss.c
+++ b/arch/m68k/mac/oss.c
@@ -1,5 +1,5 @@
 /*
- *	OSS handling
+ *	Operating System Services (OSS) chip handling
  *	Written by Joshua M. Thompson (funaho@jurai.org)
  *
  *
@@ -49,10 +49,8 @@
 	/* do this by setting the source's interrupt level to zero. */
 
 	for (i = 0; i <= OSS_NUM_SOURCES; i++) {
-		oss->irq_level[i] = OSS_IRQLEV_DISABLED;
+		oss->irq_level[i] = 0;
 	}
-	/* If we disable VIA1 here, we never really handle it... */
-	oss->irq_level[OSS_VIA1] = OSS_IRQLEV_VIA1;
 }
 
 /*
@@ -64,17 +62,13 @@
 }
 
 /*
- * Handle miscellaneous OSS interrupts. Right now that's just sound
- * and SCSI; everything else is routed to its own autovector IRQ.
+ * Handle miscellaneous OSS interrupts.
  */
 
 static void oss_irq(unsigned int irq, struct irq_desc *desc)
 {
-	int events;
-
-	events = oss->irq_pending & (OSS_IP_SOUND|OSS_IP_SCSI);
-	if (!events)
-		return;
+	int events = oss->irq_pending &
+	             (OSS_IP_IOPSCC | OSS_IP_SCSI | OSS_IP_IOPISM);
 
 #ifdef DEBUG_IRQS
 	if ((console_loglevel == 10) && !(events & OSS_IP_SCSI)) {
@@ -82,16 +76,20 @@
 			(int) oss->irq_pending);
 	}
 #endif
-	/* FIXME: how do you clear a pending IRQ?    */
 
-	if (events & OSS_IP_SOUND) {
-		oss->irq_pending &= ~OSS_IP_SOUND;
-		/* FIXME: call sound handler */
-	} else if (events & OSS_IP_SCSI) {
+	if (events & OSS_IP_IOPSCC) {
+		oss->irq_pending &= ~OSS_IP_IOPSCC;
+		generic_handle_irq(IRQ_MAC_SCC);
+	}
+
+	if (events & OSS_IP_SCSI) {
 		oss->irq_pending &= ~OSS_IP_SCSI;
 		generic_handle_irq(IRQ_MAC_SCSI);
-	} else {
-		/* FIXME: error check here? */
+	}
+
+	if (events & OSS_IP_IOPISM) {
+		oss->irq_pending &= ~OSS_IP_IOPISM;
+		generic_handle_irq(IRQ_MAC_ADB);
 	}
 }
 
@@ -130,14 +128,29 @@
 
 /*
  * Register the OSS and NuBus interrupt dispatchers.
+ *
+ * This IRQ mapping is laid out with two things in mind: first, we try to keep
+ * things on their own levels to avoid having to do double-dispatches. Second,
+ * the levels match as closely as possible the alternate IRQ mapping mode (aka
+ * "A/UX mode") available on some VIA machines.
  */
 
+#define OSS_IRQLEV_IOPISM    IRQ_AUTO_1
+#define OSS_IRQLEV_SCSI      IRQ_AUTO_2
+#define OSS_IRQLEV_NUBUS     IRQ_AUTO_3
+#define OSS_IRQLEV_IOPSCC    IRQ_AUTO_4
+#define OSS_IRQLEV_VIA1      IRQ_AUTO_6
+
 void __init oss_register_interrupts(void)
 {
-	irq_set_chained_handler(OSS_IRQLEV_SCSI, oss_irq);
-	irq_set_chained_handler(OSS_IRQLEV_NUBUS, oss_nubus_irq);
-	irq_set_chained_handler(OSS_IRQLEV_SOUND, oss_irq);
-	irq_set_chained_handler(OSS_IRQLEV_VIA1, via1_irq);
+	irq_set_chained_handler(OSS_IRQLEV_IOPISM, oss_irq);
+	irq_set_chained_handler(OSS_IRQLEV_SCSI,   oss_irq);
+	irq_set_chained_handler(OSS_IRQLEV_NUBUS,  oss_nubus_irq);
+	irq_set_chained_handler(OSS_IRQLEV_IOPSCC, oss_irq);
+	irq_set_chained_handler(OSS_IRQLEV_VIA1,   via1_irq);
+
+	/* OSS_VIA1 gets enabled here because it has no machspec interrupt. */
+	oss->irq_level[OSS_VIA1] = IRQ_AUTO_6;
 }
 
 /*
@@ -156,13 +169,13 @@
 	switch(irq) {
 		case IRQ_MAC_SCC:
 			oss->irq_level[OSS_IOPSCC] = OSS_IRQLEV_IOPSCC;
-			break;
+			return;
 		case IRQ_MAC_ADB:
 			oss->irq_level[OSS_IOPISM] = OSS_IRQLEV_IOPISM;
-			break;
+			return;
 		case IRQ_MAC_SCSI:
 			oss->irq_level[OSS_SCSI] = OSS_IRQLEV_SCSI;
-			break;
+			return;
 		case IRQ_NUBUS_9:
 		case IRQ_NUBUS_A:
 		case IRQ_NUBUS_B:
@@ -171,13 +184,11 @@
 		case IRQ_NUBUS_E:
 			irq -= NUBUS_SOURCE_BASE;
 			oss->irq_level[irq] = OSS_IRQLEV_NUBUS;
-			break;
-#ifdef DEBUG_IRQUSE
-		default:
-			printk("%s unknown irq %d\n", __func__, irq);
-			break;
-#endif
+			return;
 	}
+
+	if (IRQ_SRC(irq) == 1)
+		via_irq_enable(irq);
 }
 
 /*
@@ -193,14 +204,14 @@
 #endif
 	switch(irq) {
 		case IRQ_MAC_SCC:
-			oss->irq_level[OSS_IOPSCC] = OSS_IRQLEV_DISABLED;
-			break;
+			oss->irq_level[OSS_IOPSCC] = 0;
+			return;
 		case IRQ_MAC_ADB:
-			oss->irq_level[OSS_IOPISM] = OSS_IRQLEV_DISABLED;
-			break;
+			oss->irq_level[OSS_IOPISM] = 0;
+			return;
 		case IRQ_MAC_SCSI:
-			oss->irq_level[OSS_SCSI] = OSS_IRQLEV_DISABLED;
-			break;
+			oss->irq_level[OSS_SCSI] = 0;
+			return;
 		case IRQ_NUBUS_9:
 		case IRQ_NUBUS_A:
 		case IRQ_NUBUS_B:
@@ -208,12 +219,10 @@
 		case IRQ_NUBUS_D:
 		case IRQ_NUBUS_E:
 			irq -= NUBUS_SOURCE_BASE;
-			oss->irq_level[irq] = OSS_IRQLEV_DISABLED;
-			break;
-#ifdef DEBUG_IRQUSE
-		default:
-			printk("%s unknown irq %d\n", __func__, irq);
-			break;
-#endif
+			oss->irq_level[irq] = 0;
+			return;
 	}
+
+	if (IRQ_SRC(irq) == 1)
+		via_irq_disable(irq);
 }