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);