[MIPS] Rewrite all the assembler interrupt handlers to C.

Saves like 1,600 lines of code, is way easier to debug, compilers
frequently do a better job than the cut and paste type of handlers many
boards had.  And finally having all the stuff done in a single place
also means alot of bug potencial for the MT ASE is gone.

The only surviving handler in assembler is the DECstation one; I hope
Maciej will rewrite it.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

10 files changed, 317 insertions, 375 deletions

diff --git a/arch/mips/mips-boards/atlas/Makefile b/arch/mips/mips-boards/atlas/Makefile
index 50fec2a5aee..d8dab75906b 100644
--- a/arch/mips/mips-boards/atlas/Makefile
+++ b/arch/mips/mips-boards/atlas/Makefile
@@ -16,5 +16,5 @@
 # 59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
 #
 
-obj-y			:= atlas_int.o atlas-irq.o atlas_setup.o
+obj-y			:= atlas_int.o atlas_setup.o
 obj-$(CONFIG_KGDB)	+= atlas_gdb.o
diff --git a/arch/mips/mips-boards/atlas/atlas-irq.S b/arch/mips/mips-boards/atlas/atlas-irq.S
deleted file mode 100644
index 31bc99a5238..00000000000
--- a/arch/mips/mips-boards/atlas/atlas-irq.S
+++ /dev/null
@@ -1,120 +0,0 @@
-/*
- * Carsten Langgaard, carstenl@mips.com
- * Copyright (C) 1999, 2000 MIPS Technologies, Inc.  All rights reserved.
- *
- *  This program is free software; you can distribute it and/or modify it
- *  under the terms of the GNU General Public License (Version 2) as
- *  published by the Free Software Foundation.
- *
- *  This program is distributed in the hope it will be useful, but WITHOUT
- *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- *  for more details.
- *
- *  You should have received a copy of the GNU General Public License along
- *  with this program; if not, write to the Free Software Foundation, Inc.,
- *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
- *
- * Interrupt exception dispatch code.
- */
-#include <linux/config.h>
-
-#include <asm/asm.h>
-#include <asm/mipsregs.h>
-#include <asm/regdef.h>
-#include <asm/stackframe.h>
-#include <asm/mips-boards/atlasint.h>
-
-/*
- * Furthermore, the IRQs on the MIPS board look basically (barring software
- * IRQs which we don't use at all and all external interrupt sources are
- * combined together on hardware interrupt 0 (MIPS IRQ 2)) like:
- *
- *	MIPS IRQ	Source
- *      --------        ------
- *             0	Software (ignored)
- *             1        Software (ignored)
- *             2        Combined hardware interrupt (hw0)
- *             3        Hardware (ignored)
- *             4        Hardware (ignored)
- *             5        Hardware (ignored)
- *             6        Hardware (ignored)
- *             7        R4k timer (what we use)
- *
- * Note: On the SEAD board thing are a little bit different.
- *       Here IRQ 2 (hw0) is wired to the UART0 and IRQ 3 (hw1) is wired
- *       wired to UART1.
- *
- * We handle the IRQ according to _our_ priority which is:
- *
- * Highest ----     R4k Timer
- * Lowest  ----     Combined hardware interrupt
- *
- * then we just return, if multiple IRQs are pending then we will just take
- * another exception, big deal.
- */
-
-	.text
-	.set	noreorder
-	.set	noat
-	.align	5
-	NESTED(mipsIRQ, PT_SIZE, sp)
-	SAVE_ALL
-	CLI
-	.set	at
-
-	mfc0	s0, CP0_CAUSE		# get irq bits
-	mfc0	s1, CP0_STATUS		# get irq mask
-	andi	s0, ST0_IM		# CAUSE.CE may be non-zero!
-	and	s0, s1
-
-#if defined(CONFIG_CPU_MIPS32) || defined(CONFIG_CPU_MIPS64)
-	.set	mips32
-	clz	a0, s0
-	.set	mips0
-	negu	a0
-	addu	a0, 31-CAUSEB_IP
-	bltz	a0, spurious
-#else
-	beqz	s0, spurious
-	 li	a0, 7
-
-	and	t0, s0, 0xf000
-	sltiu	t0, t0, 1
-	sll	t0, 2
-	subu	a0, t0
-	sll	s0, t0
-
-	and	t0, s0, 0xc000
-	sltiu	t0, t0, 1
-	sll	t0, 1
-	subu	a0, t0
-	sll	s0, t0
-
-	and	t0, s0, 0x8000
-	sltiu	t0, t0, 1
-	# sll	t0, 0
-	subu	a0, t0
-	# sll	s0, t0
-#endif
-
-	 li	a1, MIPSCPU_INT_ATLAS
-	bne	a0, a1, 1f
-	 addu	a0, MIPSCPU_INT_BASE
-
-	jal	atlas_hw0_irqdispatch
-	 move	 a0, sp
-
-	j	ret_from_irq
-	 nop
-
-1:	jal	do_IRQ
-	 move	a1, sp
-
-	j	ret_from_irq
-	 nop
-
-spurious:
-	j	spurious_interrupt
-	 nop
-	END(mipsIRQ)
diff --git a/arch/mips/mips-boards/atlas/atlas_int.c b/arch/mips/mips-boards/atlas/atlas_int.c
index bc0ebc69bfb..db53950b7cf 100644
--- a/arch/mips/mips-boards/atlas/atlas_int.c
+++ b/arch/mips/mips-boards/atlas/atlas_int.c
@@ -39,8 +39,6 @@
 
 static struct atlas_ictrl_regs *atlas_hw0_icregs;
 
-extern asmlinkage void mipsIRQ(void);
-
 #if 0
 #define DEBUG_INT(x...) printk(x)
 #else
@@ -98,7 +96,7 @@ static inline int ls1bit32(unsigned int x)
 	return b;
 }
 
-void atlas_hw0_irqdispatch(struct pt_regs *regs)
+static inline void atlas_hw0_irqdispatch(struct pt_regs *regs)
 {
 	unsigned long int_status;
 	int irq;
@@ -116,6 +114,91 @@ void atlas_hw0_irqdispatch(struct pt_regs *regs)
 	do_IRQ(irq, regs);
 }
 
+static inline int clz(unsigned long x)
+{
+	__asm__ (
+	"	.set	push					\n"
+	"	.set	mips32					\n"
+	"	clz	%0, %1					\n"
+	"	.set	pop					\n"
+	: "=r" (x)
+	: "r" (x));
+
+	return x;
+}
+
+/*
+ * Version of ffs that only looks at bits 12..15.
+ */
+static inline unsigned int irq_ffs(unsigned int pending)
+{
+#if defined(CONFIG_CPU_MIPS32) || defined(CONFIG_CPU_MIPS64)
+	return -clz(pending) + 31 - CAUSEB_IP;
+#else
+	unsigned int a0 = 7;
+	unsigned int t0;
+
+	t0 = s0 & 0xf000;
+	t0 = t0 < 1;
+	t0 = t0 << 2;
+	a0 = a0 - t0;
+	s0 = s0 << t0;
+
+	t0 = s0 & 0xc000;
+	t0 = t0 < 1;
+	t0 = t0 << 1;
+	a0 = a0 - t0;
+	s0 = s0 << t0;
+
+	t0 = s0 & 0x8000;
+	t0 = t0 < 1;
+	//t0 = t0 << 2;
+	a0 = a0 - t0;
+	//s0 = s0 << t0;
+
+	return a0;
+#endif
+}
+
+/*
+ * IRQs on the Atlas board look basically (barring software IRQs which we
+ * don't use at all and all external interrupt sources are combined together
+ * on hardware interrupt 0 (MIPS IRQ 2)) like:
+ *
+ *	MIPS IRQ	Source
+ *      --------        ------
+ *             0	Software (ignored)
+ *             1        Software (ignored)
+ *             2        Combined hardware interrupt (hw0)
+ *             3        Hardware (ignored)
+ *             4        Hardware (ignored)
+ *             5        Hardware (ignored)
+ *             6        Hardware (ignored)
+ *             7        R4k timer (what we use)
+ *
+ * We handle the IRQ according to _our_ priority which is:
+ *
+ * Highest ----     R4k Timer
+ * Lowest  ----     Combined hardware interrupt
+ *
+ * then we just return, if multiple IRQs are pending then we will just take
+ * another exception, big deal.
+ */
+asmlinkage void plat_irq_dispatch(struct pt_regs *regs)
+{
+	unsigned int pending = read_c0_cause() & read_c0_status() & ST0_IM;
+	int irq;
+
+	irq = irq_ffs(pending);
+
+	if (irq == MIPSCPU_INT_ATLAS)
+		atlas_hw0_irqdispatch(regs);
+	else if (irq > 0)
+		do_IRQ(MIPSCPU_INT_BASE + irq, regs);
+	else
+		spurious_interrupt(regs);
+}
+
 void __init arch_init_irq(void)
 {
 	int i;
@@ -128,9 +211,6 @@ void __init arch_init_irq(void)
 	 */
 	atlas_hw0_icregs->intrsten = 0xffffffff;
 
-	/* Now safe to set the exception vector. */
-	set_except_vector(0, mipsIRQ);
-
 	for (i = ATLASINT_BASE; i <= ATLASINT_END; i++) {
 		irq_desc[i].status	= IRQ_DISABLED;
 		irq_desc[i].action	= 0;
diff --git a/arch/mips/mips-boards/malta/Makefile b/arch/mips/mips-boards/malta/Makefile
index 3ae8fe6c007..fd4c143c0e2 100644
--- a/arch/mips/mips-boards/malta/Makefile
+++ b/arch/mips/mips-boards/malta/Makefile
@@ -19,4 +19,4 @@
 # under Linux.
 #
 
-obj-y := malta_int.o malta-irq.o malta_setup.o
+obj-y := malta_int.o malta_setup.o
diff --git a/arch/mips/mips-boards/malta/malta-irq.S b/arch/mips/mips-boards/malta/malta-irq.S
deleted file mode 100644
index 6217aff3be0..00000000000
--- a/arch/mips/mips-boards/malta/malta-irq.S
+++ /dev/null
@@ -1,122 +0,0 @@
-/*
- * Carsten Langgaard, carstenl@mips.com
- * Copyright (C) 1999, 2000 MIPS Technologies, Inc.  All rights reserved.
- *
- * ########################################################################
- *
- *  This program is free software; you can distribute it and/or modify it
- *  under the terms of the GNU General Public License (Version 2) as
- *  published by the Free Software Foundation.
- *
- *  This program is distributed in the hope it will be useful, but WITHOUT
- *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- *  for more details.
- *
- *  You should have received a copy of the GNU General Public License along
- *  with this program; if not, write to the Free Software Foundation, Inc.,
- *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
- *
- * ########################################################################
- *
- * Interrupt exception dispatch code.
- *
- */
-#include <linux/config.h>
-
-#include <asm/asm.h>
-#include <asm/mipsregs.h>
-#include <asm/regdef.h>
-#include <asm/stackframe.h>
-#include <asm/mips-boards/maltaint.h>
-
-/*
- * IRQs on the Malta board look basically (barring software IRQs which we
- * don't use at all and all external interrupt sources are combined together
- * on hardware interrupt 0 (MIPS IRQ 2)) like:
- *
- *	MIPS IRQ	Source
- *      --------        ------
- *             0	Software (ignored)
- *             1        Software (ignored)
- *             2        Combined hardware interrupt (hw0)
- *             3        Hardware (ignored)
- *             4        Hardware (ignored)
- *             5        Hardware (ignored)
- *             6        Hardware (ignored)
- *             7        R4k timer (what we use)
- *
- * We handle the IRQ according to _our_ priority which is:
- *
- * Highest ----     R4k Timer
- * Lowest  ----     Combined hardware interrupt
- *
- * then we just return, if multiple IRQs are pending then we will just take
- * another exception, big deal.
- */
-
-	.text
-	.set	noreorder
-	.set	noat
-	.align	5
-	NESTED(mipsIRQ, PT_SIZE, sp)
-	SAVE_ALL
-	CLI
-	.set	at
-
-	mfc0	s0, CP0_CAUSE		# get irq bits
-	mfc0	s1, CP0_STATUS		# get irq mask
-	andi	s0, ST0_IM		# CAUSE.CE may be non-zero!
-	and	s0, s1
-
-#if defined(CONFIG_CPU_MIPS32) || defined(CONFIG_CPU_MIPS64)
- 	.set	mips32
-	clz	a0, s0
-	.set	mips0
-	negu	a0
-	addu	a0, 31-CAUSEB_IP
-	bltz	a0, spurious
-#else
-	beqz	s0, spurious
-	 li	a0, 7
-
-	and	t0, s0, 0xf000
-	sltiu	t0, t0, 1
-	sll	t0, 2
-	subu	a0, t0
-	sll	s0, t0
-
-	and	t0, s0, 0xc000
-	sltiu	t0, t0, 1
-	sll	t0, 1
-	subu	a0, t0
-	sll	s0, t0
-
-	and	t0, s0, 0x8000
-	sltiu	t0, t0, 1
-	# sll	t0, 0
-	subu	a0, t0
-	# sll	s0, t0
-#endif
-
-	 li	a1, MIPSCPU_INT_I8259A
-	bne	a0, a1, 1f
-	 addu	a0, MIPSCPU_INT_BASE
-
-	jal	malta_hw0_irqdispatch
-	 move	 a0, sp
-
-	j	ret_from_irq
-	 nop
-1:
-
-	jal	do_IRQ
-	 move	a1, sp
-
-	j	ret_from_irq
-	 nop
-
-spurious:
-	j	spurious_interrupt
-	 nop
-	END(mipsIRQ)
diff --git a/arch/mips/mips-boards/malta/malta_int.c b/arch/mips/mips-boards/malta/malta_int.c
index d06dc5ad6c9..1da8c18b9c8 100644
--- a/arch/mips/mips-boards/malta/malta_int.c
+++ b/arch/mips/mips-boards/malta/malta_int.c
@@ -40,7 +40,6 @@
 #include <asm/mips-boards/msc01_pci.h>
 #include <asm/msc01_ic.h>
 
-extern asmlinkage void mipsIRQ(void);
 extern void mips_timer_interrupt(void);
 
 static DEFINE_SPINLOCK(mips_irq_lock);
@@ -114,7 +113,7 @@ static inline int get_int(void)
 	return irq;
 }
 
-void malta_hw0_irqdispatch(struct pt_regs *regs)
+static void malta_hw0_irqdispatch(struct pt_regs *regs)
 {
 	int irq;
 
@@ -182,6 +181,92 @@ void corehi_irqdispatch(struct pt_regs *regs)
         die("CoreHi interrupt", regs);
 }
 
+static inline int clz(unsigned long x)
+{
+	__asm__ (
+	"	.set	push					\n"
+	"	.set	mips32					\n"
+	"	clz	%0, %1					\n"
+	"	.set	pop					\n"
+	: "=r" (x)
+	: "r" (x));
+
+	return x;
+}
+
+/*
+ * Version of ffs that only looks at bits 12..15.
+ */
+static inline unsigned int irq_ffs(unsigned int pending)
+{
+#if defined(CONFIG_CPU_MIPS32) || defined(CONFIG_CPU_MIPS64)
+	return -clz(pending) + 31 - CAUSEB_IP;
+#else
+	unsigned int a0 = 7;
+	unsigned int t0;
+
+	t0 = s0 & 0xf000;
+	t0 = t0 < 1;
+	t0 = t0 << 2;
+	a0 = a0 - t0;
+	s0 = s0 << t0;
+
+	t0 = s0 & 0xc000;
+	t0 = t0 < 1;
+	t0 = t0 << 1;
+	a0 = a0 - t0;
+	s0 = s0 << t0;
+
+	t0 = s0 & 0x8000;
+	t0 = t0 < 1;
+	//t0 = t0 << 2;
+	a0 = a0 - t0;
+	//s0 = s0 << t0;
+
+	return a0;
+#endif
+}
+
+/*
+ * IRQs on the Malta board look basically (barring software IRQs which we
+ * don't use at all and all external interrupt sources are combined together
+ * on hardware interrupt 0 (MIPS IRQ 2)) like:
+ *
+ *	MIPS IRQ	Source
+ *      --------        ------
+ *             0	Software (ignored)
+ *             1        Software (ignored)
+ *             2        Combined hardware interrupt (hw0)
+ *             3        Hardware (ignored)
+ *             4        Hardware (ignored)
+ *             5        Hardware (ignored)
+ *             6        Hardware (ignored)
+ *             7        R4k timer (what we use)
+ *
+ * We handle the IRQ according to _our_ priority which is:
+ *
+ * Highest ----     R4k Timer
+ * Lowest  ----     Combined hardware interrupt
+ *
+ * then we just return, if multiple IRQs are pending then we will just take
+ * another exception, big deal.
+ */
+
+asmlinkage void plat_irq_dispatch(struct pt_regs *regs)
+{
+	unsigned int pending = read_c0_cause() & read_c0_status() & ST0_IM;
+	int irq;
+
+	irq = irq_ffs(pending);
+
+	if (irq == MIPSCPU_INT_I8259A)
+		malta_hw0_irqdispatch(regs);
+	else if (irq > 0)
+		do_IRQ(MIPSCPU_INT_BASE + irq, regs);
+	else
+		spurious_interrupt(regs);
+}
+
 static struct irqaction i8259irq = {
 	.handler = no_action,
 	.name = "XT-PIC cascade"
@@ -214,7 +299,6 @@ int __initdata msc_nr_eicirqs = sizeof(msc_eicirqmap)/sizeof(msc_irqmap_t);
 
 void __init arch_init_irq(void)
 {
-	set_except_vector(0, mipsIRQ);
 	init_i8259_irqs();
 
 	if (!cpu_has_veic)
@@ -245,7 +329,6 @@ void __init arch_init_irq(void)
 		setup_irq (MIPSCPU_INT_BASE+MIPSCPU_INT_COREHI, &corehi_irqaction);
 	}
 	else {
-		set_except_vector(0, mipsIRQ);
 		setup_irq (MIPSCPU_INT_BASE+MIPSCPU_INT_I8259A, &i8259irq);
 		setup_irq (MIPSCPU_INT_BASE+MIPSCPU_INT_COREHI, &corehi_irqaction);
 	}
diff --git a/arch/mips/mips-boards/sead/Makefile b/arch/mips/mips-boards/sead/Makefile
index 01780b60534..224bb848f16 100644
--- a/arch/mips/mips-boards/sead/Makefile
+++ b/arch/mips/mips-boards/sead/Makefile
@@ -23,4 +23,4 @@
 # under Linux.
 #
 
-obj-y		:= sead_int.o sead-irq.o sead_setup.o
+obj-y		:= sead_int.o sead_setup.o
diff --git a/arch/mips/mips-boards/sead/sead-irq.S b/arch/mips/mips-boards/sead/sead-irq.S
deleted file mode 100644
index d5dea1d2e22..00000000000
--- a/arch/mips/mips-boards/sead/sead-irq.S
+++ /dev/null
@@ -1,111 +0,0 @@
-/*
- * Carsten Langgaard, carstenl@mips.com
- * Copyright (C) 1999, 2000 MIPS Technologies, Inc.  All rights reserved.
- *
- * ########################################################################
- *
- *  This program is free software; you can distribute it and/or modify it
- *  under the terms of the GNU General Public License (Version 2) as
- *  published by the Free Software Foundation.
- *
- *  This program is distributed in the hope it will be useful, but WITHOUT
- *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- *  for more details.
- *
- *  You should have received a copy of the GNU General Public License along
- *  with this program; if not, write to the Free Software Foundation, Inc.,
- *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
- *
- * ########################################################################
- *
- * Interrupt exception dispatch code.
- *
- */
-#include <linux/config.h>
-
-#include <asm/asm.h>
-#include <asm/mipsregs.h>
-#include <asm/regdef.h>
-#include <asm/stackframe.h>
-#include <asm/mips-boards/seadint.h>
-
-/*
- * IRQs on the SEAD board look basically are combined together on hardware
- * interrupt 0 (MIPS IRQ 2)) like:
- *
- *	MIPS IRQ	Source
- *      --------        ------
- *             0	Software (ignored)
- *             1        Software (ignored)
- *             2        UART0 (hw0)
- *             3        UART1 (hw1)
- *             4        Hardware (ignored)
- *             5        Hardware (ignored)
- *             6        Hardware (ignored)
- *             7        R4k timer (what we use)
- *
- * We handle the IRQ according to _our_ priority which is:
- *
- * Highest ----     R4k Timer
- * Lowest  ----     Combined hardware interrupt
- *
- * then we just return, if multiple IRQs are pending then we will just take
- * another exception, big deal.
- */
-
-	.text
-	.set	noreorder
-	.set	noat
-	.align	5
-	NESTED(mipsIRQ, PT_SIZE, sp)
-	SAVE_ALL
-	CLI
-	.set	at
-
-	mfc0	s0, CP0_CAUSE		# get irq bits
-	mfc0	s1, CP0_STATUS		# get irq mask
-	andi	s0, ST0_IM		# CAUSE.CE may be non-zero!
-	and	s0, s1
-
-#if defined(CONFIG_CPU_MIPS32) || defined(CONFIG_CPU_MIPS64)
- 	.set	mips32
-	clz	a0, s0
-	.set	mips0
-	negu	a0
-	addu	a0, 31-CAUSEB_IP
-	bltz	a0, spurious
-#else
-	beqz	s0, spurious
-	 li	a0, 7
-
-	and	t0, s0, 0xf000
-	sltiu	t0, t0, 1
-	sll	t0, 2
-	subu	a0, t0
-	sll	s0, t0
-
-	and	t0, s0, 0xc000
-	sltiu	t0, t0, 1
-	sll	t0, 1
-	subu	a0, t0
-	sll	s0, t0
-
-	and	t0, s0, 0x8000
-	sltiu	t0, t0, 1
-	# sll	t0, 0
-	subu	a0, t0
-	# sll	s0, t0
-#endif
-
-	 addu	a0, MIPSCPU_INT_BASE
-	jal	do_IRQ
-	 move	a1, sp
-
-	j	ret_from_irq
-	 nop
-
-spurious:
-	j	spurious_interrupt
-	 nop
-	END(mipsIRQ)
diff --git a/arch/mips/mips-boards/sead/sead_int.c b/arch/mips/mips-boards/sead/sead_int.c
index 90fda0d9915..9168d934c66 100644
--- a/arch/mips/mips-boards/sead/sead_int.c
+++ b/arch/mips/mips-boards/sead/sead_int.c
@@ -24,16 +24,94 @@
 #include <linux/irq.h>
 
 #include <asm/irq_cpu.h>
+#include <asm/mipsregs.h>
 #include <asm/system.h>
 
 #include <asm/mips-boards/seadint.h>
 
-extern asmlinkage void mipsIRQ(void);
+static inline int clz(unsigned long x)
+{
+	__asm__ (
+	"	.set	push					\n"
+	"	.set	mips32					\n"
+	"	clz	%0, %1					\n"
+	"	.set	pop					\n"
+	: "=r" (x)
+	: "r" (x));
+
+	return x;
+}
+
+/*
+ * Version of ffs that only looks at bits 12..15.
+ */
+static inline unsigned int irq_ffs(unsigned int pending)
+{
+#if defined(CONFIG_CPU_MIPS32) || defined(CONFIG_CPU_MIPS64)
+	return -clz(pending) + 31 - CAUSEB_IP;
+#else
+	unsigned int a0 = 7;
+	unsigned int t0;
+
+	t0 = s0 & 0xf000;
+	t0 = t0 < 1;
+	t0 = t0 << 2;
+	a0 = a0 - t0;
+	s0 = s0 << t0;
+
+	t0 = s0 & 0xc000;
+	t0 = t0 < 1;
+	t0 = t0 << 1;
+	a0 = a0 - t0;
+	s0 = s0 << t0;
+
+	t0 = s0 & 0x8000;
+	t0 = t0 < 1;
+	//t0 = t0 << 2;
+	a0 = a0 - t0;
+	//s0 = s0 << t0;
+
+	return a0;
+#endif
+}
+
+/*
+ * IRQs on the SEAD board look basically are combined together on hardware
+ * interrupt 0 (MIPS IRQ 2)) like:
+ *
+ *	MIPS IRQ	Source
+ *      --------        ------
+ *             0	Software (ignored)
+ *             1        Software (ignored)
+ *             2        UART0 (hw0)
+ *             3        UART1 (hw1)
+ *             4        Hardware (ignored)
+ *             5        Hardware (ignored)
+ *             6        Hardware (ignored)
+ *             7        R4k timer (what we use)
+ *
+ * We handle the IRQ according to _our_ priority which is:
+ *
+ * Highest ----     R4k Timer
+ * Lowest  ----     Combined hardware interrupt
+ *
+ * then we just return, if multiple IRQs are pending then we will just take
+ * another exception, big deal.
+ */
+asmlinkage void plat_irq_dispatch(struct pt_regs *regs)
+{
+	unsigned int pending = read_c0_cause() & read_c0_status() & ST0_IM;
+	int irq;
+
+	irq = irq_ffs(pending);
+
+	if (irq >= 0)
+		do_IRQ(MIPSCPU_INT_BASE + irq, regs);
+	else
+		spurious_interrupt(regs);
+}
 
 void __init arch_init_irq(void)
 {
 	mips_cpu_irq_init(MIPSCPU_INT_BASE);
-
-	/* Now safe to set the exception vector. */
-	set_except_vector(0, mipsIRQ);
 }
diff --git a/arch/mips/mips-boards/sim/sim_int.c b/arch/mips/mips-boards/sim/sim_int.c
index a4d0a2c0503..2c15c8efec4 100644
--- a/arch/mips/mips-boards/sim/sim_int.c
+++ b/arch/mips/mips-boards/sim/sim_int.c
@@ -25,17 +25,71 @@
 
 extern void mips_cpu_irq_init(int);
 
-extern asmlinkage void simIRQ(void);
+static inline int clz(unsigned long x)
+{
+	__asm__ (
+	"	.set	push					\n"
+	"	.set	mips32					\n"
+	"	clz	%0, %1					\n"
+	"	.set	pop					\n"
+	: "=r" (x)
+	: "r" (x));
+
+	return x;
+}
+
+/*
+ * Version of ffs that only looks at bits 12..15.
+ */
+static inline unsigned int irq_ffs(unsigned int pending)
+{
+#if defined(CONFIG_CPU_MIPS32) || defined(CONFIG_CPU_MIPS64)
+	return -clz(pending) + 31 - CAUSEB_IP;
+#else
+	unsigned int a0 = 7;
+	unsigned int t0;
+
+	t0 = s0 & 0xf000;
+	t0 = t0 < 1;
+	t0 = t0 << 2;
+	a0 = a0 - t0;
+	s0 = s0 << t0;
+
+	t0 = s0 & 0xc000;
+	t0 = t0 < 1;
+	t0 = t0 << 1;
+	a0 = a0 - t0;
+	s0 = s0 << t0;
 
-asmlinkage void sim_hw0_irqdispatch(struct pt_regs *regs)
+	t0 = s0 & 0x8000;
+	t0 = t0 < 1;
+	//t0 = t0 << 2;
+	a0 = a0 - t0;
+	//s0 = s0 << t0;
+
+	return a0;
+#endif
+}
+
+static inline void sim_hw0_irqdispatch(struct pt_regs *regs)
 {
 	do_IRQ(2, regs);
 }
 
-void __init arch_init_irq(void)
+asmlinkage void plat_irq_dispatch(struct pt_regs *regs)
 {
-	/* Now safe to set the exception vector. */
-	set_except_vector(0, simIRQ);
+	unsigned int pending = read_c0_cause() & read_c0_status() & ST0_IM;
+	int irq;
+
+	irq = irq_ffs(pending);
 
+	if (irq > 0)
+		do_IRQ(MIPSCPU_INT_BASE + irq, regs);
+	else
+		spurious_interrupt(regs);
+}
+
+void __init arch_init_irq(void)
+{
 	mips_cpu_irq_init(MIPSCPU_INT_BASE);
 }