Virtual SMP support for the 34K.

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

7 files changed, 448 insertions, 13 deletions

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 5af30d385aca..8746e1b1621b 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -1344,6 +1344,14 @@ config CPU_HAS_PREFETCH
 config MIPS_MT
 	bool "Enable MIPS MT"
 
+choice
+	prompt "MIPS MT options"
+	depends on MIPS_MT
+
+config MIPS_MT_SMP
+	bool "Use 1 TC on each available VPE for SMP"
+	select SMP
+
 config MIPS_VPE_LOADER
 	bool "VPE loader support."
 	depends on MIPS_MT
@@ -1351,6 +1359,8 @@ config MIPS_VPE_LOADER
 	  Includes a loader for loading an elf relocatable object
 	  onto another VPE and running it.
 
+endchoice
+
 config MIPS_VPE_LOADER_TOM
 	bool "Load VPE program into memory hidden from linux"
 	depends on MIPS_VPE_LOADER
@@ -1496,7 +1506,7 @@ source "mm/Kconfig"
 
 config SMP
 	bool "Multi-Processing support"
-	depends on CPU_RM9000 || (SIBYTE_SB1250 && !SIBYTE_STANDALONE) || SGI_IP27
+	depends on CPU_RM9000 || (SIBYTE_SB1250 && !SIBYTE_STANDALONE) || SGI_IP27 || MIPS_MT_SMP
 	---help---
 	  This enables support for systems with more than one CPU. If you have
 	  a system with only one CPU, like most personal computers, say N. If
diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 0f527063a8a8..4c09e1acafd7 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -34,6 +34,8 @@ obj-$(CONFIG_CPU_R6000)		+= r6000_fpu.o r4k_switch.o
 
 obj-$(CONFIG_SMP)		+= smp.o
 
+obj-$(CONFIG_MIPS_MT_SMP)	+= smp_mt.o
+
 obj-$(CONFIG_MIPS_VPE_LOADER)	+= vpe.o
 obj-$(CONFIG_MIPS_VPE_APSP_API)	+= rtlx.o
 
diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
index fd904d1e4190..aa18a8b7b380 100644
--- a/arch/mips/kernel/genex.S
+++ b/arch/mips/kernel/genex.S
@@ -323,6 +323,7 @@ NESTED(nmi_handler, PT_SIZE, sp)
 	BUILD_HANDLER mdmx mdmx sti silent		/* #22 */
 	BUILD_HANDLER watch watch sti verbose		/* #23 */
 	BUILD_HANDLER mcheck mcheck cli verbose		/* #24 */
+	BUILD_HANDLER mt mt sti verbose			/* #25 */
 	BUILD_HANDLER dsp dsp sti silent		/* #26 */
 	BUILD_HANDLER reserved reserved sti verbose	/* others */
 
diff --git a/arch/mips/kernel/smp_mt.c b/arch/mips/kernel/smp_mt.c
new file mode 100644
index 000000000000..d429544ba4bc
--- /dev/null
+++ b/arch/mips/kernel/smp_mt.c
@@ -0,0 +1,366 @@
+/*
+ * Copyright (C) 2004, 2005 MIPS Technologies, Inc.  All rights reserved.
+ *
+ *  Elizabeth Clarke (beth@mips.com)
+ *
+ *  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.
+ *
+ */
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/cpumask.h>
+#include <linux/interrupt.h>
+#include <linux/compiler.h>
+
+#include <asm/atomic.h>
+#include <asm/cpu.h>
+#include <asm/processor.h>
+#include <asm/system.h>
+#include <asm/hardirq.h>
+#include <asm/mmu_context.h>
+#include <asm/smp.h>
+#include <asm/time.h>
+#include <asm/mipsregs.h>
+#include <asm/mipsmtregs.h>
+#include <asm/cacheflush.h>
+#include <asm/mips-boards/maltaint.h>
+
+#define MIPS_CPU_IPI_RESCHED_IRQ 0
+#define MIPS_CPU_IPI_CALL_IRQ 1
+
+static int cpu_ipi_resched_irq, cpu_ipi_call_irq;
+
+#if 0
+static void dump_mtregisters(int vpe, int tc)
+{
+	printk("vpe %d tc %d\n", vpe, tc);
+
+	settc(tc);
+
+	printk("  c0 status  0x%lx\n", read_vpe_c0_status());
+	printk("  vpecontrol 0x%lx\n", read_vpe_c0_vpecontrol());
+	printk("  vpeconf0    0x%lx\n", read_vpe_c0_vpeconf0());
+	printk("  tcstatus 0x%lx\n", read_tc_c0_tcstatus());
+	printk("  tcrestart 0x%lx\n", read_tc_c0_tcrestart());
+	printk("  tcbind 0x%lx\n", read_tc_c0_tcbind());
+	printk("  tchalt 0x%lx\n", read_tc_c0_tchalt());
+}
+#endif
+
+void __init sanitize_tlb_entries(void)
+{
+	int i, tlbsiz;
+	unsigned long mvpconf0, ncpu;
+
+	if (!cpu_has_mipsmt)
+		return;
+
+	set_c0_mvpcontrol(MVPCONTROL_VPC);
+
+	/* Disable TLB sharing */
+	clear_c0_mvpcontrol(MVPCONTROL_STLB);
+
+	mvpconf0 = read_c0_mvpconf0();
+
+	printk(KERN_INFO "MVPConf0 0x%lx TLBS %lx PTLBE %ld\n", mvpconf0,
+		   (mvpconf0 & MVPCONF0_TLBS) >> MVPCONF0_TLBS_SHIFT,
+			   (mvpconf0 & MVPCONF0_PTLBE) >> MVPCONF0_PTLBE_SHIFT);
+
+	tlbsiz = (mvpconf0 & MVPCONF0_PTLBE) >> MVPCONF0_PTLBE_SHIFT;
+	ncpu = ((mvpconf0 & MVPCONF0_PVPE) >> MVPCONF0_PVPE_SHIFT) + 1;
+
+	printk(" tlbsiz %d ncpu %ld\n", tlbsiz, ncpu);
+
+	if (tlbsiz > 0) {
+		/* share them out across the vpe's */
+		tlbsiz /= ncpu;
+
+		printk(KERN_INFO "setting Config1.MMU_size to %d\n", tlbsiz);
+
+		for (i = 0; i < ncpu; i++) {
+			settc(i);
+
+			if (i == 0)
+				write_c0_config1((read_c0_config1() & ~(0x3f << 25)) | (tlbsiz << 25));
+			else
+				write_vpe_c0_config1((read_vpe_c0_config1() & ~(0x3f << 25)) |
+						   (tlbsiz << 25));
+		}
+	}
+
+	clear_c0_mvpcontrol(MVPCONTROL_VPC);
+}
+
+#if 0
+/*
+ * Use c0_MVPConf0 to find out how many CPUs are available, setting up
+ * phys_cpu_present_map and the logical/physical mappings.
+ */
+void __init prom_build_cpu_map(void)
+{
+	int i, num, ncpus;
+
+	cpus_clear(phys_cpu_present_map);
+
+	/* assume we boot on cpu 0.... */
+	cpu_set(0, phys_cpu_present_map);
+	__cpu_number_map[0] = 0;
+	__cpu_logical_map[0] = 0;
+
+	if (cpu_has_mipsmt) {
+		ncpus = ((read_c0_mvpconf0() & (MVPCONF0_PVPE)) >> MVPCONF0_PVPE_SHIFT) + 1;
+		for (i=1, num=0; i< NR_CPUS && i<ncpus; i++) {
+			cpu_set(i, phys_cpu_present_map);
+			__cpu_number_map[i] = ++num;
+			__cpu_logical_map[num] = i;
+		}
+
+		printk(KERN_INFO "%i available secondary CPU(s)\n", num);
+	}
+}
+#endif
+
+static void ipi_resched_dispatch (struct pt_regs *regs)
+{
+	do_IRQ(MIPS_CPU_IPI_RESCHED_IRQ, regs);
+}
+
+static void ipi_call_dispatch (struct pt_regs *regs)
+{
+	do_IRQ(MIPS_CPU_IPI_CALL_IRQ, regs);
+}
+
+irqreturn_t ipi_resched_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+{
+	return IRQ_HANDLED;
+}
+
+irqreturn_t ipi_call_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+{
+	smp_call_function_interrupt();
+
+	return IRQ_HANDLED;
+}
+
+static struct irqaction irq_resched = {
+	.handler	= ipi_resched_interrupt,
+	.flags		= SA_INTERRUPT,
+	.name		= "IPI_resched"
+};
+
+static struct irqaction irq_call = {
+	.handler	= ipi_call_interrupt,
+	.flags		= SA_INTERRUPT,
+	.name		= "IPI_call"
+};
+
+/*
+ * Common setup before any secondaries are started
+ * Make sure all CPU's are in a sensible state before we boot any of the
+ * secondarys
+ */
+void prom_prepare_cpus(unsigned int max_cpus)
+{
+	unsigned long val;
+	int i, num;
+
+	if (!cpu_has_mipsmt)
+		return;
+
+	/* disable MT so we can configure */
+	dvpe();
+	dmt();
+
+	/* Put MVPE's into 'configuration state' */
+	set_c0_mvpcontrol(MVPCONTROL_VPC);
+
+	val = read_c0_mvpconf0();
+
+	/* we'll always have more TC's than VPE's, so loop setting everything
+	   to a sensible state */
+	for (i = 0, num = 0; i <= ((val & MVPCONF0_PTC) >> MVPCONF0_PTC_SHIFT); i++) {
+		settc(i);
+
+		/* VPE's */
+		if (i <= ((val & MVPCONF0_PVPE) >> MVPCONF0_PVPE_SHIFT)) {
+
+			/* deactivate all but vpe0 */
+			if (i != 0) {
+				unsigned long tmp = read_vpe_c0_vpeconf0();
+
+				tmp &= ~VPECONF0_VPA;
+
+				/* master VPE */
+				tmp |= VPECONF0_MVP;
+				write_vpe_c0_vpeconf0(tmp);
+
+				/* Record this as available CPU */
+				if (i < max_cpus) {
+					cpu_set(i, phys_cpu_present_map);
+					__cpu_number_map[i]	= ++num;
+					__cpu_logical_map[num]	= i;
+				}
+			}
+
+			/* disable multi-threading with TC's */
+			write_vpe_c0_vpecontrol(read_vpe_c0_vpecontrol() & ~VPECONTROL_TE);
+
+			if (i != 0) {
+				write_vpe_c0_status((read_c0_status() & ~(ST0_IM | ST0_IE | ST0_KSU)) | ST0_CU0);
+				write_vpe_c0_cause(read_vpe_c0_cause() & ~CAUSEF_IP);
+
+				/* set config to be the same as vpe0, particularly kseg0 coherency alg */
+				write_vpe_c0_config( read_c0_config());
+			}
+
+		}
+
+		/* TC's */
+
+		if (i != 0) {
+			unsigned long tmp;
+
+			/* bind a TC to each VPE, May as well put all excess TC's
+			   on the last VPE */
+			if ( i >= (((val & MVPCONF0_PVPE) >> MVPCONF0_PVPE_SHIFT)+1) )
+				write_tc_c0_tcbind(read_tc_c0_tcbind() | ((val & MVPCONF0_PVPE) >> MVPCONF0_PVPE_SHIFT) );
+			else {
+				write_tc_c0_tcbind( read_tc_c0_tcbind() | i);
+
+				/* and set XTC */
+				write_vpe_c0_vpeconf0( read_vpe_c0_vpeconf0() | (i << VPECONF0_XTC_SHIFT));
+			}
+
+			tmp = read_tc_c0_tcstatus();
+
+			/* mark not allocated and not dynamically allocatable */
+			tmp &= ~(TCSTATUS_A | TCSTATUS_DA);
+			tmp |= TCSTATUS_IXMT;		/* interrupt exempt */
+			write_tc_c0_tcstatus(tmp);
+
+			write_tc_c0_tchalt(TCHALT_H);
+		}
+	}
+
+	/* Release config state */
+	clear_c0_mvpcontrol(MVPCONTROL_VPC);
+
+	/* We'll wait until starting the secondaries before starting MVPE */
+
+	printk(KERN_INFO "Detected %i available secondary CPU(s)\n", num);
+
+	/* set up ipi interrupts */
+	if (cpu_has_vint) {
+		set_vi_handler (MIPS_CPU_IPI_RESCHED_IRQ, ipi_resched_dispatch);
+		set_vi_handler (MIPS_CPU_IPI_CALL_IRQ, ipi_call_dispatch);
+	}
+
+	cpu_ipi_resched_irq = MIPSCPU_INT_BASE + MIPS_CPU_IPI_RESCHED_IRQ;
+	cpu_ipi_call_irq = MIPSCPU_INT_BASE + MIPS_CPU_IPI_CALL_IRQ;
+
+	setup_irq(cpu_ipi_resched_irq, &irq_resched);
+	setup_irq(cpu_ipi_call_irq, &irq_call);
+
+	/* need to mark IPI's as IRQ_PER_CPU */
+	irq_desc[cpu_ipi_resched_irq].status |= IRQ_PER_CPU;
+	irq_desc[cpu_ipi_call_irq].status |= IRQ_PER_CPU;
+}
+
+/*
+ * Setup the PC, SP, and GP of a secondary processor and start it
+ * running!
+ * smp_bootstrap is the place to resume from
+ * __KSTK_TOS(idle) is apparently the stack pointer
+ * (unsigned long)idle->thread_info the gp
+ * assumes a 1:1 mapping of TC => VPE
+ */
+void prom_boot_secondary(int cpu, struct task_struct *idle)
+{
+	dvpe();
+	set_c0_mvpcontrol(MVPCONTROL_VPC);
+
+	settc(cpu);
+
+	/* restart */
+	write_tc_c0_tcrestart((unsigned long)&smp_bootstrap);
+
+	/* enable the tc this vpe/cpu will be running */
+	write_tc_c0_tcstatus((read_tc_c0_tcstatus() & ~TCSTATUS_IXMT) | TCSTATUS_A);
+
+	write_tc_c0_tchalt(0);
+
+	/* enable the VPE */
+	write_vpe_c0_vpeconf0(read_vpe_c0_vpeconf0() | VPECONF0_VPA);
+
+	/* stack pointer */
+	write_tc_gpr_sp( __KSTK_TOS(idle));
+
+	/* global pointer */
+	write_tc_gpr_gp((unsigned long)idle->thread_info);
+
+	flush_icache_range((unsigned long)idle->thread_info,
+					   (unsigned long)idle->thread_info +
+					   sizeof(struct thread_info));
+
+	/* finally out of configuration and into chaos */
+	clear_c0_mvpcontrol(MVPCONTROL_VPC);
+
+	evpe(EVPE_ENABLE);
+}
+
+void prom_init_secondary(void)
+{
+	write_c0_status((read_c0_status() & ~ST0_IM ) |
+	                (STATUSF_IP0 | STATUSF_IP1 | STATUSF_IP7));
+}
+
+void prom_smp_finish(void)
+{
+	write_c0_compare(read_c0_count() + (8* mips_hpt_frequency/HZ));
+
+	local_irq_enable();
+}
+
+void prom_cpus_done(void)
+{
+}
+
+void core_send_ipi(int cpu, unsigned int action)
+{
+	int i;
+	unsigned long flags;
+	int vpflags;
+
+	local_irq_save (flags);
+
+	vpflags = dvpe();	/* cant access the other CPU's registers whilst MVPE enabled */
+
+	switch (action) {
+	case SMP_CALL_FUNCTION:
+		i = C_SW1;
+		break;
+
+	case SMP_RESCHEDULE_YOURSELF:
+	default:
+		i = C_SW0;
+		break;
+	}
+
+	/* 1:1 mapping of vpe and tc... */
+	settc(cpu);
+	write_vpe_c0_cause(read_vpe_c0_cause() | i);
+	evpe(vpflags);
+
+	local_irq_restore(flags);
+}
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 876aff71cd2e..e38f24b2b3db 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -28,6 +28,8 @@
 #include <asm/cpu.h>
 #include <asm/dsp.h>
 #include <asm/fpu.h>
+#include <asm/mipsregs.h>
+#include <asm/mipsmtregs.h>
 #include <asm/module.h>
 #include <asm/pgtable.h>
 #include <asm/ptrace.h>
@@ -56,6 +58,7 @@ extern asmlinkage void handle_tr(void);
 extern asmlinkage void handle_fpe(void);
 extern asmlinkage void handle_mdmx(void);
 extern asmlinkage void handle_watch(void);
+extern asmlinkage void handle_mt(void);
 extern asmlinkage void handle_dsp(void);
 extern asmlinkage void handle_mcheck(void);
 extern asmlinkage void handle_reserved(void);
@@ -797,6 +800,14 @@ asmlinkage void do_mcheck(struct pt_regs *regs)
 	      (regs->cp0_status & ST0_TS) ? "" : "not ");
 }
 
+asmlinkage void do_mt(struct pt_regs *regs)
+{
+	die_if_kernel("MIPS MT Thread exception in kernel", regs);
+
+	force_sig(SIGILL, current);
+}
+
+
 asmlinkage void do_dsp(struct pt_regs *regs)
 {
 	if (cpu_has_dsp)
@@ -1338,6 +1349,9 @@ void __init trap_init(void)
 	if (cpu_has_mcheck)
 		set_except_vector(24, handle_mcheck);
 
+	if (cpu_has_mipsmt)
+		set_except_vector(25, handle_mt);
+
 	if (cpu_has_dsp)
 		set_except_vector(26, handle_dsp);
 
diff --git a/arch/mips/kernel/vpe.c b/arch/mips/kernel/vpe.c
index 6bf42ba08f09..97fefcc9dbe7 100644
--- a/arch/mips/kernel/vpe.c
+++ b/arch/mips/kernel/vpe.c
@@ -32,7 +32,7 @@
  * mknod /dev/vpe0 c 63 0
  * mknod /dev/vpe1 c 63 1
  */
-
+#include <linux/config.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/fs.h>
@@ -49,6 +49,7 @@
 #include <linux/poll.h>
 #include <linux/bootmem.h>
 #include <asm/mipsregs.h>
+#include <asm/mipsmtregs.h>
 #include <asm/cacheflush.h>
 #include <asm/atomic.h>
 #include <asm/cpu.h>
@@ -697,7 +698,7 @@ int vpe_run(vpe_t * v)
 	dvpe();
 
 	/* Put MVPE's into 'configuration state' */
-	write_c0_mvpcontrol(read_c0_mvpcontrol() | MVPCONTROL_VPC);
+	set_c0_mvpcontrol(MVPCONTROL_VPC);
 
 	if (!list_empty(&v->tc)) {
 		if ((t = list_entry(v->tc.next, struct tc, tc)) == NULL) {
@@ -760,7 +761,7 @@ int vpe_run(vpe_t * v)
 	write_vpe_c0_cause(0);
 
 	/* take system out of configuration state */
-	write_c0_mvpcontrol(read_c0_mvpcontrol() & ~MVPCONTROL_VPC);
+	clear_c0_mvpcontrol(MVPCONTROL_VPC);
 
 	/* clear interrupts enabled IE, ERL, EXL, and KSU from c0 status */
 	write_vpe_c0_status(read_vpe_c0_status() & ~(ST0_ERL | ST0_KSU | ST0_IE | ST0_EXL));
@@ -1134,7 +1135,7 @@ int vpe_free(vpe_handle vpe)
 	evpe_flags = dvpe();
 
 	/* Put MVPE's into 'configuration state' */
-	write_c0_mvpcontrol(read_c0_mvpcontrol() | MVPCONTROL_VPC);
+	set_c0_mvpcontrol(MVPCONTROL_VPC);
 
 	settc(t->index);
 	write_vpe_c0_vpeconf0(read_vpe_c0_vpeconf0() & ~VPECONF0_VPA);
@@ -1145,7 +1146,7 @@ int vpe_free(vpe_handle vpe)
 
 	v->state = VPE_STATE_UNUSED;
 
-	write_c0_mvpcontrol(read_c0_mvpcontrol() & ~MVPCONTROL_VPC);
+	clear_c0_mvpcontrol(MVPCONTROL_VPC);
 	evpe(evpe_flags);
 
 	return 0;
@@ -1191,7 +1192,7 @@ static int __init vpe_module_init(void)
 	dvpe();
 
 	/* Put MVPE's into 'configuration state' */
-	write_c0_mvpcontrol(read_c0_mvpcontrol() | MVPCONTROL_VPC);
+	set_c0_mvpcontrol(MVPCONTROL_VPC);
 
 	/* dump_mtregs(); */
 
@@ -1270,7 +1271,7 @@ static int __init vpe_module_init(void)
 	}
 
 	/* release config state */
-	write_c0_mvpcontrol(read_c0_mvpcontrol() & ~MVPCONTROL_VPC);
+	clear_c0_mvpcontrol(MVPCONTROL_VPC);
 
 	return 0;
 }
diff --git a/arch/mips/mips-boards/generic/time.c b/arch/mips/mips-boards/generic/time.c
index 3a6f1428b2cb..72a12d931cba 100644
--- a/arch/mips/mips-boards/generic/time.c
+++ b/arch/mips/mips-boards/generic/time.c
@@ -61,6 +61,15 @@ static unsigned int display_count = 0;
 static unsigned int timer_tick_count=0;
 static int mips_cpu_timer_irq;
 
+static inline void scroll_display_message(void)
+{
+	if ((timer_tick_count++ % HZ) == 0) {
+		mips_display_message(&display_string[display_count++]);
+		if (display_count == MAX_DISPLAY_COUNT)
+			display_count = 0;
+	}
+}
+
 static void mips_timer_dispatch (struct pt_regs *regs)
 {
 	do_IRQ (mips_cpu_timer_irq, regs);
@@ -68,17 +77,42 @@ static void mips_timer_dispatch (struct pt_regs *regs)
 
 irqreturn_t mips_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 {
+#ifdef CONFIG_SMP
+	int cpu = smp_processor_id();
+
+	if (cpu == 0) {
+		/*
+		 * CPU 0 handles the global timer interrupt job and process accounting
+		 * resets count/compare registers to trigger next timer int.
+		 */
+		(void) timer_interrupt(irq, dev_id, regs);
+		scroll_display_message();
+	}
+	else {
+		/* Everyone else needs to reset the timer int here as
+		   ll_local_timer_interrupt doesn't */
+		/*
+		 * FIXME: need to cope with counter underflow.
+		 * More support needs to be added to kernel/time for
+		 * counter/timer interrupts on multiple CPU's
+		 */
+		write_c0_compare (read_c0_count() + (mips_hpt_frequency/HZ));
+		/*
+		 * other CPUs should do profiling and process accounting
+		 */
+		local_timer_interrupt (irq, dev_id, regs);
+	}
+
+	return IRQ_HANDLED;
+#else
 	irqreturn_t r;
 
 	r = timer_interrupt(irq, dev_id, regs);
 
-	if ((timer_tick_count++ % HZ) == 0) {
-		mips_display_message(&display_string[display_count++]);
-		if (display_count == MAX_DISPLAY_COUNT)
-			display_count = 0;
-	}
+	scroll_display_message();
 
 	return r;
+#endif
 }
 
 /*
@@ -176,6 +210,13 @@ void __init mips_timer_setup(struct irqaction *irq)
 	irq->handler = mips_timer_interrupt;	/* we use our own handler */
 	setup_irq(mips_cpu_timer_irq, irq);
 
+#ifdef CONFIG_SMP
+	/* irq_desc(riptor) is a global resource, when the interrupt overlaps
+	   on seperate cpu's the first one tries to handle the second interrupt.
+	   The effect is that the int remains disabled on the second cpu.
+	   Mark the interrupt with IRQ_PER_CPU to avoid any confusion */
+	irq_desc[mips_cpu_timer_irq].status |= IRQ_PER_CPU;
+#endif
 
         /* to generate the first timer interrupt */
 	write_c0_compare (read_c0_count() + mips_hpt_frequency/HZ);