generic: sparse irqs: use irq_desc() together with dyn_array, instead of irq_desc[]

add CONFIG_HAVE_SPARSE_IRQ to for use condensed array.
Get rid of irq_desc[] array assumptions.

Preallocate 32 irq_desc, and irq_desc() will try to get more.

( No change in functionality is expected anywhere, except the odd build
  failure where we missed a code site or where a crossing commit itroduces
  new irq_desc[] usage. )

v2: according to Eric, change get_irq_desc() to irq_desc()

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

28 files changed, 404 insertions, 187 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index c1f9febb404f..b36762246265 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -105,3 +105,7 @@ config HAVE_CLK
 
 config HAVE_DYN_ARRAY
         def_bool n
+
+config HAVE_SPARSE_IRQ
+        def_bool n
+
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 42f98009d752..1004888e9b13 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -34,6 +34,7 @@ config X86
         select HAVE_GENERIC_DMA_COHERENT if X86_32
         select HAVE_EFFICIENT_UNALIGNED_ACCESS
         select HAVE_DYN_ARRAY
+        select HAVE_SPARSE_IRQ if X86_64
 
 config ARCH_DEFCONFIG
         string
diff --git a/arch/x86/kernel/io_apic_32.c b/arch/x86/kernel/io_apic_32.c
index 7f2bcc3dad82..c2160cfdec9b 100644
--- a/arch/x86/kernel/io_apic_32.c
+++ b/arch/x86/kernel/io_apic_32.c
@@ -345,6 +345,7 @@ static void set_ioapic_affinity_irq(unsigned int irq, cpumask_t cpumask)
         struct irq_pin_list *entry = irq_2_pin + irq;
         unsigned int apicid_value;
         cpumask_t tmp;
+        struct irq_desc *desc;
 
         cpus_and(tmp, cpumask, cpu_online_map);
         if (cpus_empty(tmp))
@@ -365,7 +366,8 @@ static void set_ioapic_affinity_irq(unsigned int irq, cpumask_t cpumask)
                         break;
                 entry = irq_2_pin + entry->next;
         }
-        irq_desc[irq].affinity = cpumask;
+        desc = irq_to_desc(irq);
+        desc->affinity = cpumask;
         spin_unlock_irqrestore(&ioapic_lock, flags);
 }
 
@@ -475,10 +477,12 @@ static inline void balance_irq(int cpu, int irq)
 static inline void rotate_irqs_among_cpus(unsigned long useful_load_threshold)
 {
         int i, j;
+        struct irq_desc *desc;
 
         for_each_online_cpu(i) {
                 for (j = 0; j < nr_irqs; j++) {
-                        if (!irq_desc[j].action)
+                        desc = irq_to_desc(j);
+                        if (!desc->action)
                                 continue;
                         /* Is it a significant load ?  */
                         if (IRQ_DELTA(CPU_TO_PACKAGEINDEX(i), j) <
@@ -505,6 +509,7 @@ static void do_irq_balance(void)
         unsigned long tmp_cpu_irq;
         unsigned long imbalance = 0;
         cpumask_t allowed_mask, target_cpu_mask, tmp;
+        struct irq_desc *desc;
 
         for_each_possible_cpu(i) {
                 int package_index;
@@ -515,7 +520,8 @@ static void do_irq_balance(void)
                 for (j = 0; j < nr_irqs; j++) {
                         unsigned long value_now, delta;
                         /* Is this an active IRQ or balancing disabled ? */
-                        if (!irq_desc[j].action || irq_balancing_disabled(j))
+                        desc = irq_to_desc(j);
+                        if (!desc->action || irq_balancing_disabled(j))
                                 continue;
                         if (package_index == i)
                                 IRQ_DELTA(package_index, j) = 0;
@@ -609,7 +615,8 @@ tryanotherirq:
         selected_irq = -1;
         for (j = 0; j < nr_irqs; j++) {
                 /* Is this an active IRQ? */
-                if (!irq_desc[j].action)
+                desc = irq_to_desc(j);
+                if (!desc->action)
                         continue;
                 if (imbalance <= IRQ_DELTA(max_loaded, j))
                         continue;
@@ -682,10 +689,12 @@ static int balanced_irq(void *unused)
         int i;
         unsigned long prev_balance_time = jiffies;
         long time_remaining = balanced_irq_interval;
+        struct irq_desc *desc;
 
         /* push everything to CPU 0 to give us a starting point.  */
         for (i = 0 ; i < nr_irqs ; i++) {
-                irq_desc[i].pending_mask = cpumask_of_cpu(0);
+                desc = irq_to_desc(i);
+                desc->pending_mask = cpumask_of_cpu(0);
                 set_pending_irq(i, cpumask_of_cpu(0));
         }
 
@@ -1254,13 +1263,16 @@ static struct irq_chip ioapic_chip;
 
 static void ioapic_register_intr(int irq, int vector, unsigned long trigger)
 {
+        struct irq_desc *desc;
+
+        desc = irq_to_desc(irq);
         if ((trigger == IOAPIC_AUTO && IO_APIC_irq_trigger(irq)) ||
             trigger == IOAPIC_LEVEL) {
-                irq_desc[irq].status |= IRQ_LEVEL;
+                desc->status |= IRQ_LEVEL;
                 set_irq_chip_and_handler_name(irq, &ioapic_chip,
                                          handle_fasteoi_irq, "fasteoi");
         } else {
-                irq_desc[irq].status &= ~IRQ_LEVEL;
+                desc->status &= ~IRQ_LEVEL;
                 set_irq_chip_and_handler_name(irq, &ioapic_chip,
                                          handle_edge_irq, "edge");
         }
@@ -2027,6 +2039,7 @@ static struct irq_chip ioapic_chip __read_mostly = {
 static inline void init_IO_APIC_traps(void)
 {
         int irq;
+        struct irq_desc *desc;
 
         /*
          * NOTE! The local APIC isn't very good at handling
@@ -2048,9 +2061,11 @@ static inline void init_IO_APIC_traps(void)
                          */
                         if (irq < 16)
                                 make_8259A_irq(irq);
-                        else
+                        else {
+                                desc = irq_to_desc(irq);
                                 /* Strange. Oh, well.. */
-                                irq_desc[irq].chip = &no_irq_chip;
+                                desc->chip = &no_irq_chip;
+                        }
                 }
         }
 }
@@ -2089,7 +2104,10 @@ static struct irq_chip lapic_chip __read_mostly = {
 
 static void lapic_register_intr(int irq, int vector)
 {
-        irq_desc[irq].status &= ~IRQ_LEVEL;
+        struct irq_desc *desc;
+
+        desc = irq_to_desc(irq);
+        desc->status &= ~IRQ_LEVEL;
         set_irq_chip_and_handler_name(irq, &lapic_chip, handle_edge_irq,
                                       "edge");
         set_intr_gate(vector, interrupt[irq]);
@@ -2556,6 +2574,7 @@ static void set_msi_irq_affinity(unsigned int irq, cpumask_t mask)
         unsigned int dest;
         cpumask_t tmp;
         int vector;
+        struct irq_desc *desc;
 
         cpus_and(tmp, mask, cpu_online_map);
         if (cpus_empty(tmp))
@@ -2575,7 +2594,8 @@ static void set_msi_irq_affinity(unsigned int irq, cpumask_t mask)
         msg.address_lo |= MSI_ADDR_DEST_ID(dest);
 
         write_msi_msg(irq, &msg);
-        irq_desc[irq].affinity = mask;
+        desc = irq_to_desc(irq);
+        desc->affinity = mask;
 }
 #endif /* CONFIG_SMP */
 
@@ -2649,6 +2669,7 @@ static void set_ht_irq_affinity(unsigned int irq, cpumask_t mask)
 {
         unsigned int dest;
         cpumask_t tmp;
+        struct irq_desc *desc;
 
         cpus_and(tmp, mask, cpu_online_map);
         if (cpus_empty(tmp))
@@ -2659,7 +2680,8 @@ static void set_ht_irq_affinity(unsigned int irq, cpumask_t mask)
         dest = cpu_mask_to_apicid(mask);
 
         target_ht_irq(irq, dest);
-        irq_desc[irq].affinity = mask;
+        desc = irq_to_desc(irq);
+        desc->affinity = mask;
 }
 #endif
 
diff --git a/arch/x86/kernel/io_apic_64.c b/arch/x86/kernel/io_apic_64.c
index 93a3ffabfe6a..cab5a25d81b1 100644
--- a/arch/x86/kernel/io_apic_64.c
+++ b/arch/x86/kernel/io_apic_64.c
@@ -345,6 +345,7 @@ static void set_ioapic_affinity_irq(unsigned int irq, cpumask_t mask)
         unsigned long flags;
         unsigned int dest;
         cpumask_t tmp;
+        struct irq_desc *desc;
 
         cpus_and(tmp, mask, cpu_online_map);
         if (cpus_empty(tmp))
@@ -361,9 +362,10 @@ static void set_ioapic_affinity_irq(unsigned int irq, cpumask_t mask)
          */
         dest = SET_APIC_LOGICAL_ID(dest);
 
+        desc = irq_to_desc(irq);
         spin_lock_irqsave(&ioapic_lock, flags);
         __target_IO_APIC_irq(irq, dest, cfg->vector);
-        irq_desc[irq].affinity = mask;
+        desc->affinity = mask;
         spin_unlock_irqrestore(&ioapic_lock, flags);
 }
 #endif
@@ -933,14 +935,17 @@ static struct irq_chip ir_ioapic_chip;
 
 static void ioapic_register_intr(int irq, unsigned long trigger)
 {
+        struct irq_desc *desc;
+
+        desc = irq_to_desc(irq);
         if (trigger)
-                irq_desc[irq].status |= IRQ_LEVEL;
+                desc->status |= IRQ_LEVEL;
         else
-                irq_desc[irq].status &= ~IRQ_LEVEL;
+                desc->status &= ~IRQ_LEVEL;
 
 #ifdef CONFIG_INTR_REMAP
         if (irq_remapped(irq)) {
-                irq_desc[irq].status |= IRQ_MOVE_PCNTXT;
+                desc->status |= IRQ_MOVE_PCNTXT;
                 if (trigger)
                         set_irq_chip_and_handler_name(irq, &ir_ioapic_chip,
                                                       handle_fasteoi_irq,
@@ -1596,10 +1601,10 @@ static DECLARE_DELAYED_WORK(ir_migration_work, ir_irq_migration);
 static void migrate_ioapic_irq(int irq, cpumask_t mask)
 {
         struct irq_cfg *cfg = irq_cfg + irq;
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc;
         cpumask_t tmp, cleanup_mask;
         struct irte irte;
-        int modify_ioapic_rte = desc->status & IRQ_LEVEL;
+        int modify_ioapic_rte;
         unsigned int dest;
         unsigned long flags;
 
@@ -1616,6 +1621,8 @@ static void migrate_ioapic_irq(int irq, cpumask_t mask)
         cpus_and(tmp, cfg->domain, mask);
         dest = cpu_mask_to_apicid(tmp);
 
+        desc = irq_to_desc(irq);
+        modify_ioapic_rte = desc->status & IRQ_LEVEL;
         if (modify_ioapic_rte) {
                 spin_lock_irqsave(&ioapic_lock, flags);
                 __target_IO_APIC_irq(irq, dest, cfg->vector);
@@ -1637,12 +1644,13 @@ static void migrate_ioapic_irq(int irq, cpumask_t mask)
                 cfg->move_in_progress = 0;
         }
 
-        irq_desc[irq].affinity = mask;
+        desc->affinity = mask;
 }
 
 static int migrate_irq_remapped_level(int irq)
 {
         int ret = -1;
+        struct irq_desc *desc = irq_to_desc(irq);
 
         mask_IO_APIC_irq(irq);
 
@@ -1658,11 +1666,11 @@ static int migrate_irq_remapped_level(int irq)
         }
 
         /* everthing is clear. we have right of way */
-        migrate_ioapic_irq(irq, irq_desc[irq].pending_mask);
+        migrate_ioapic_irq(irq, desc->pending_mask);
 
         ret = 0;
-        irq_desc[irq].status &= ~IRQ_MOVE_PENDING;
-        cpus_clear(irq_desc[irq].pending_mask);
+        desc->status &= ~IRQ_MOVE_PENDING;
+        cpus_clear(desc->pending_mask);
 
 unmask:
         unmask_IO_APIC_irq(irq);
@@ -1674,7 +1682,7 @@ static void ir_irq_migration(struct work_struct *work)
         int irq;
 
         for (irq = 0; irq < nr_irqs; irq++) {
-                struct irq_desc *desc = irq_desc + irq;
+                struct irq_desc *desc = irq_to_desc(irq);
                 if (desc->status & IRQ_MOVE_PENDING) {
                         unsigned long flags;
 
@@ -1686,8 +1694,7 @@ static void ir_irq_migration(struct work_struct *work)
                                 continue;
                         }
 
-                        desc->chip->set_affinity(irq,
-                                                 irq_desc[irq].pending_mask);
+                        desc->chip->set_affinity(irq, desc->pending_mask);
                         spin_unlock_irqrestore(&desc->lock, flags);
                 }
         }
@@ -1698,9 +1705,11 @@ static void ir_irq_migration(struct work_struct *work)
  */
 static void set_ir_ioapic_affinity_irq(unsigned int irq, cpumask_t mask)
 {
-        if (irq_desc[irq].status & IRQ_LEVEL) {
-                irq_desc[irq].status |= IRQ_MOVE_PENDING;
-                irq_desc[irq].pending_mask = mask;
+        struct irq_desc *desc = irq_to_desc(irq);
+
+        if (desc->status & IRQ_LEVEL) {
+                desc->status |= IRQ_MOVE_PENDING;
+                desc->pending_mask = mask;
                 migrate_irq_remapped_level(irq);
                 return;
         }
@@ -1725,7 +1734,7 @@ asmlinkage void smp_irq_move_cleanup_interrupt(void)
                 if (irq >= nr_irqs)
                         continue;
 
-                desc = irq_desc + irq;
+                desc = irq_to_desc(irq);
                 cfg = irq_cfg + irq;
                 spin_lock(&desc->lock);
                 if (!cfg->move_cleanup_count)
@@ -1791,7 +1800,7 @@ static void ack_apic_level(unsigned int irq)
         irq_complete_move(irq);
 #ifdef CONFIG_GENERIC_PENDING_IRQ
         /* If we are moving the irq we need to mask it */
-        if (unlikely(irq_desc[irq].status & IRQ_MOVE_PENDING)) {
+        if (unlikely(irq_to_desc(irq)->status & IRQ_MOVE_PENDING)) {
                 do_unmask_irq = 1;
                 mask_IO_APIC_irq(irq);
         }
@@ -1868,6 +1877,7 @@ static struct irq_chip ir_ioapic_chip __read_mostly = {
 static inline void init_IO_APIC_traps(void)
 {
         int irq;
+        struct irq_desc *desc;
 
         /*
          * NOTE! The local APIC isn't very good at handling
@@ -1889,9 +1899,11 @@ static inline void init_IO_APIC_traps(void)
                          */
                         if (irq < 16)
                                 make_8259A_irq(irq);
-                        else
+                        else {
+                                desc = irq_to_desc(irq);
                                 /* Strange. Oh, well.. */
-                                irq_desc[irq].chip = &no_irq_chip;
+                                desc->chip = &no_irq_chip;
+                        }
                 }
         }
 }
@@ -1926,7 +1938,10 @@ static struct irq_chip lapic_chip __read_mostly = {
 
 static void lapic_register_intr(int irq)
 {
-        irq_desc[irq].status &= ~IRQ_LEVEL;
+        struct irq_desc *desc;
+
+        desc = irq_to_desc(irq);
+        desc->status &= ~IRQ_LEVEL;
         set_irq_chip_and_handler_name(irq, &lapic_chip, handle_edge_irq,
                                       "edge");
 }
@@ -2402,6 +2417,7 @@ static void set_msi_irq_affinity(unsigned int irq, cpumask_t mask)
         struct msi_msg msg;
         unsigned int dest;
         cpumask_t tmp;
+        struct irq_desc *desc;
 
         cpus_and(tmp, mask, cpu_online_map);
         if (cpus_empty(tmp))
@@ -2421,7 +2437,8 @@ static void set_msi_irq_affinity(unsigned int irq, cpumask_t mask)
         msg.address_lo |= MSI_ADDR_DEST_ID(dest);
 
         write_msi_msg(irq, &msg);
-        irq_desc[irq].affinity = mask;
+        desc = irq_to_desc(irq);
+        desc->affinity = mask;
 }
 
 #ifdef CONFIG_INTR_REMAP
@@ -2435,6 +2452,7 @@ static void ir_set_msi_irq_affinity(unsigned int irq, cpumask_t mask)
         unsigned int dest;
         cpumask_t tmp, cleanup_mask;
         struct irte irte;
+        struct irq_desc *desc;
 
         cpus_and(tmp, mask, cpu_online_map);
         if (cpus_empty(tmp))
@@ -2469,7 +2487,8 @@ static void ir_set_msi_irq_affinity(unsigned int irq, cpumask_t mask)
                 cfg->move_in_progress = 0;
         }
 
-        irq_desc[irq].affinity = mask;
+        desc = irq_to_desc(irq);
+        desc->affinity = mask;
 }
 #endif
 #endif /* CONFIG_SMP */
@@ -2543,7 +2562,7 @@ static int setup_msi_irq(struct pci_dev *dev, struct msi_desc *desc, int irq)
 
 #ifdef CONFIG_INTR_REMAP
         if (irq_remapped(irq)) {
-                struct irq_desc *desc = irq_desc + irq;
+                struct irq_desc *desc = irq_to_desc(irq);
                 /*
                  * irq migration in process context
                  */
@@ -2655,6 +2674,7 @@ static void dmar_msi_set_affinity(unsigned int irq, cpumask_t mask)
         struct msi_msg msg;
         unsigned int dest;
         cpumask_t tmp;
+        struct irq_desc *desc;
 
         cpus_and(tmp, mask, cpu_online_map);
         if (cpus_empty(tmp))
@@ -2674,7 +2694,8 @@ static void dmar_msi_set_affinity(unsigned int irq, cpumask_t mask)
         msg.address_lo |= MSI_ADDR_DEST_ID(dest);
 
         dmar_msi_write(irq, &msg);
-        irq_desc[irq].affinity = mask;
+        desc = irq_to_desc(irq);
+        desc->affinity = mask;
 }
 #endif /* CONFIG_SMP */
 
@@ -2731,6 +2752,7 @@ static void set_ht_irq_affinity(unsigned int irq, cpumask_t mask)
         struct irq_cfg *cfg = irq_cfg + irq;
         unsigned int dest;
         cpumask_t tmp;
+        struct irq_desc *desc;
 
         cpus_and(tmp, mask, cpu_online_map);
         if (cpus_empty(tmp))
@@ -2743,7 +2765,8 @@ static void set_ht_irq_affinity(unsigned int irq, cpumask_t mask)
         dest = cpu_mask_to_apicid(tmp);
 
         target_ht_irq(irq, dest, cfg->vector);
-        irq_desc[irq].affinity = mask;
+        desc = irq_to_desc(irq);
+        desc->affinity = mask;
 }
 #endif
 
diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
index 4c7ffb32854c..ede513be517d 100644
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -224,7 +224,7 @@ unsigned int do_IRQ(struct pt_regs *regs)
         struct pt_regs *old_regs;
         /* high bit used in ret_from_ code */
         int overflow, irq = ~regs->orig_ax;
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
 
         if (unlikely((unsigned)irq >= nr_irqs)) {
                 printk(KERN_EMERG "%s: cannot handle IRQ %d\n",
@@ -273,15 +273,16 @@ int show_interrupts(struct seq_file *p, void *v)
 
         if (i < nr_irqs) {
                 unsigned any_count = 0;
+                struct irq_desc *desc = irq_to_desc(i);
 
-                spin_lock_irqsave(&irq_desc[i].lock, flags);
+                spin_lock_irqsave(&desc->lock, flags);
 #ifndef CONFIG_SMP
                 any_count = kstat_irqs(i);
 #else
                 for_each_online_cpu(j)
                         any_count |= kstat_cpu(j).irqs[i];
 #endif
-                action = irq_desc[i].action;
+                action = desc->action;
                 if (!action && !any_count)
                         goto skip;
                 seq_printf(p, "%3d: ",i);
@@ -291,8 +292,8 @@ int show_interrupts(struct seq_file *p, void *v)
                 for_each_online_cpu(j)
                         seq_printf(p, "%10u ", kstat_cpu(j).irqs[i]);
 #endif
-                seq_printf(p, " %8s", irq_desc[i].chip->name);
-                seq_printf(p, "-%-8s", irq_desc[i].name);
+                seq_printf(p, " %8s", desc->chip->name);
+                seq_printf(p, "-%-8s", desc->name);
 
                 if (action) {
                         seq_printf(p, "  %s", action->name);
@@ -302,7 +303,7 @@ int show_interrupts(struct seq_file *p, void *v)
 
                 seq_putc(p, '\n');
 skip:
-                spin_unlock_irqrestore(&irq_desc[i].lock, flags);
+                spin_unlock_irqrestore(&desc->lock, flags);
         } else if (i == nr_irqs) {
                 seq_printf(p, "NMI: ");
                 for_each_online_cpu(j)
@@ -398,17 +399,20 @@ void fixup_irqs(cpumask_t map)
 
         for (irq = 0; irq < nr_irqs; irq++) {
                 cpumask_t mask;
+                struct irq_desc *desc;
+
                 if (irq == 2)
                         continue;
 
-                cpus_and(mask, irq_desc[irq].affinity, map);
+                desc = irq_to_desc(irq);
+                cpus_and(mask, desc->affinity, map);
                 if (any_online_cpu(mask) == NR_CPUS) {
                         printk("Breaking affinity for irq %i\n", irq);
                         mask = map;
                 }
-                if (irq_desc[irq].chip->set_affinity)
-                        irq_desc[irq].chip->set_affinity(irq, mask);
-                else if (irq_desc[irq].action && !(warned++))
+                if (desc->chip->set_affinity)
+                        desc->chip->set_affinity(irq, mask);
+                else if (desc->action && !(warned++))
                         printk("Cannot set affinity for irq %i\n", irq);
         }
 
diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
index e1f0839430d2..738eb65a924e 100644
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -83,15 +83,16 @@ int show_interrupts(struct seq_file *p, void *v)
 
         if (i < nr_irqs) {
                 unsigned any_count = 0;
+                struct irq_desc *desc = irq_to_desc(i);
 
-                spin_lock_irqsave(&irq_desc[i].lock, flags);
+                spin_lock_irqsave(&desc->lock, flags);
 #ifndef CONFIG_SMP
                 any_count = kstat_irqs(i);
 #else
                 for_each_online_cpu(j)
                         any_count |= kstat_cpu(j).irqs[i];
 #endif
-                action = irq_desc[i].action;
+                action = desc->action;
                 if (!action && !any_count)
                         goto skip;
                 seq_printf(p, "%3d: ",i);
@@ -101,8 +102,8 @@ int show_interrupts(struct seq_file *p, void *v)
                 for_each_online_cpu(j)
                         seq_printf(p, "%10u ", kstat_cpu(j).irqs[i]);
 #endif
-                seq_printf(p, " %8s", irq_desc[i].chip->name);
-                seq_printf(p, "-%-8s", irq_desc[i].name);
+                seq_printf(p, " %8s", desc->chip->name);
+                seq_printf(p, "-%-8s", desc->name);
 
                 if (action) {
                         seq_printf(p, "  %s", action->name);
@@ -111,7 +112,7 @@ int show_interrupts(struct seq_file *p, void *v)
                 }
                 seq_putc(p, '\n');
 skip:
-                spin_unlock_irqrestore(&irq_desc[i].lock, flags);
+                spin_unlock_irqrestore(&desc->lock, flags);
         } else if (i == nr_irqs) {
                 seq_printf(p, "NMI: ");
                 for_each_online_cpu(j)
@@ -228,37 +229,39 @@ void fixup_irqs(cpumask_t map)
                 cpumask_t mask;
                 int break_affinity = 0;
                 int set_affinity = 1;
+                struct irq_desc *desc;
 
                 if (irq == 2)
                         continue;
 
+                desc = irq_to_desc(irq);
                 /* interrupt's are disabled at this point */
-                spin_lock(&irq_desc[irq].lock);
+                spin_lock(&desc->lock);
 
                 if (!irq_has_action(irq) ||
-                    cpus_equal(irq_desc[irq].affinity, map)) {
-                        spin_unlock(&irq_desc[irq].lock);
+                    cpus_equal(desc->affinity, map)) {
+                        spin_unlock(&desc->lock);
                         continue;
                 }
 
-                cpus_and(mask, irq_desc[irq].affinity, map);
+                cpus_and(mask, desc->affinity, map);
                 if (cpus_empty(mask)) {
                         break_affinity = 1;
                         mask = map;
                 }
 
-                if (irq_desc[irq].chip->mask)
-                        irq_desc[irq].chip->mask(irq);
+                if (desc->chip->mask)
+                        desc->chip->mask(irq);
 
-                if (irq_desc[irq].chip->set_affinity)
-                        irq_desc[irq].chip->set_affinity(irq, mask);
+                if (desc->chip->set_affinity)
+                        desc->chip->set_affinity(irq, mask);
                 else if (!(warned++))
                         set_affinity = 0;
 
-                if (irq_desc[irq].chip->unmask)
-                        irq_desc[irq].chip->unmask(irq);
+                if (desc->chip->unmask)
+                        desc->chip->unmask(irq);
 
-                spin_unlock(&irq_desc[irq].lock);
+                spin_unlock(&desc->lock);
 
                 if (break_affinity && set_affinity)
                         printk("Broke affinity for irq %i\n", irq);
diff --git a/arch/x86/kernel/irqinit_64.c b/arch/x86/kernel/irqinit_64.c
index 165c5d9b0d1a..0744b49b4d12 100644
--- a/arch/x86/kernel/irqinit_64.c
+++ b/arch/x86/kernel/irqinit_64.c
@@ -143,9 +143,11 @@ void __init init_ISA_irqs(void)
         init_8259A(0);
 
         for (i = 0; i < nr_irqs; i++) {
-                irq_desc[i].status = IRQ_DISABLED;
-                irq_desc[i].action = NULL;
-                irq_desc[i].depth = 1;
+                struct irq_desc *desc = irq_to_desc(i);
+
+                desc->status = IRQ_DISABLED;
+                desc->action = NULL;
+                desc->depth = 1;
 
                 if (i < 16) {
                         /*
@@ -157,7 +159,7 @@ void __init init_ISA_irqs(void)
                         /*
                          * 'high' PCI IRQs filled in on demand
                          */
-                        irq_desc[i].chip = &no_irq_chip;
+                        desc->chip = &no_irq_chip;
                 }
         }
 }
diff --git a/arch/x86/kernel/visws_quirks.c b/arch/x86/kernel/visws_quirks.c
index 61a97e616f70..9d85ab384435 100644
--- a/arch/x86/kernel/visws_quirks.c
+++ b/arch/x86/kernel/visws_quirks.c
@@ -484,10 +484,11 @@ static void disable_cobalt_irq(unsigned int irq)
 static unsigned int startup_cobalt_irq(unsigned int irq)
 {
         unsigned long flags;
+        struct irq_desc *desc = irq_to_desc(irq);
 
         spin_lock_irqsave(&cobalt_lock, flags);
-        if ((irq_desc[irq].status & (IRQ_DISABLED | IRQ_INPROGRESS | IRQ_WAITING)))
-                irq_desc[irq].status &= ~(IRQ_DISABLED | IRQ_INPROGRESS | IRQ_WAITING);
+        if ((desc->status & (IRQ_DISABLED | IRQ_INPROGRESS | IRQ_WAITING)))
+                desc->status &= ~(IRQ_DISABLED | IRQ_INPROGRESS | IRQ_WAITING);
         enable_cobalt_irq(irq);
         spin_unlock_irqrestore(&cobalt_lock, flags);
         return 0;
@@ -506,9 +507,10 @@ static void ack_cobalt_irq(unsigned int irq)
 static void end_cobalt_irq(unsigned int irq)
 {
         unsigned long flags;
+        struct irq_desc *desc = irq_to_desc(irq);
 
         spin_lock_irqsave(&cobalt_lock, flags);
-        if (!(irq_desc[irq].status & (IRQ_DISABLED | IRQ_INPROGRESS)))
+        if (!(desc->status & (IRQ_DISABLED | IRQ_INPROGRESS)))
                 enable_cobalt_irq(irq);
         spin_unlock_irqrestore(&cobalt_lock, flags);
 }
@@ -626,7 +628,7 @@ static irqreturn_t piix4_master_intr(int irq, void *dev_id)
 
         spin_unlock_irqrestore(&i8259A_lock, flags);
 
-        desc = irq_desc + realirq;
+        desc = irq_to_desc(realirq);
 
         /*
          * handle this 'virtual interrupt' as a Cobalt one now.
@@ -662,27 +664,29 @@ void init_VISWS_APIC_irqs(void)
         int i;
 
         for (i = 0; i < CO_IRQ_APIC0 + CO_APIC_LAST + 1; i++) {
-                irq_desc[i].status = IRQ_DISABLED;
-                irq_desc[i].action = 0;
-                irq_desc[i].depth = 1;
+                struct irq_desc *desc = irq_to_desc(i);
+
+                desc->status = IRQ_DISABLED;
+                desc->action = 0;
+                desc->depth = 1;
 
                 if (i == 0) {
-                        irq_desc[i].chip = &cobalt_irq_type;
+                        desc->chip = &cobalt_irq_type;
                 }
                 else if (i == CO_IRQ_IDE0) {
-                        irq_desc[i].chip = &cobalt_irq_type;
+                        desc->chip = &cobalt_irq_type;
                 }
                 else if (i == CO_IRQ_IDE1) {
-                        irq_desc[i].chip = &cobalt_irq_type;
+                        desc->chip = &cobalt_irq_type;
                 }
                 else if (i == CO_IRQ_8259) {
-                        irq_desc[i].chip = &piix4_master_irq_type;
+                        desc->chip = &piix4_master_irq_type;
                 }
                 else if (i < CO_IRQ_APIC0) {
-                        irq_desc[i].chip = &piix4_virtual_irq_type;
+                        desc->chip = &piix4_virtual_irq_type;
                 }
                 else if (IS_CO_APIC(i)) {
-                        irq_desc[i].chip = &cobalt_irq_type;
+                        desc->chip = &cobalt_irq_type;
                 }
         }
 
diff --git a/arch/x86/mach-voyager/voyager_smp.c b/arch/x86/mach-voyager/voyager_smp.c
index 199a5f4a873c..0f6e8a6523ae 100644
--- a/arch/x86/mach-voyager/voyager_smp.c
+++ b/arch/x86/mach-voyager/voyager_smp.c
@@ -1483,7 +1483,7 @@ static void disable_local_vic_irq(unsigned int irq)
  * the interrupt off to another CPU */
 static void before_handle_vic_irq(unsigned int irq)
 {
-        irq_desc_t *desc = irq_desc + irq;
+        irq_desc_t *desc = irq_to_desc(irq);
         __u8 cpu = smp_processor_id();
 
         _raw_spin_lock(&vic_irq_lock);
@@ -1518,7 +1518,7 @@ static void before_handle_vic_irq(unsigned int irq)
 /* Finish the VIC interrupt: basically mask */
 static void after_handle_vic_irq(unsigned int irq)
 {
-        irq_desc_t *desc = irq_desc + irq;
+        irq_desc_t *desc = irq_to_desc(irq);
 
         _raw_spin_lock(&vic_irq_lock);
         {
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 8d2940517c99..572d372899d3 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1058,7 +1058,7 @@ static void gpiolib_dbg_show(struct seq_file *s, struct gpio_chip *chip)
 
                 if (!is_out) {
                         int             irq = gpio_to_irq(gpio);
-                        struct irq_desc *desc = irq_desc + irq;
+                        struct irq_desc *desc = irq_to_desc(irq);
 
                         /* This races with request_irq(), set_irq_type(),
                          * and set_irq_wake() ... but those are "rare".
diff --git a/drivers/mfd/asic3.c b/drivers/mfd/asic3.c
index ba5aa2008273..e4c0db4dc7b1 100644
--- a/drivers/mfd/asic3.c
+++ b/drivers/mfd/asic3.c
@@ -123,7 +123,7 @@ static void asic3_irq_demux(unsigned int irq, struct irq_desc *desc)
                                         irqnr = asic->irq_base +
                                                 (ASIC3_GPIOS_PER_BANK * bank)
                                                 + i;
-                                        desc = irq_desc + irqnr;
+                                        desc = irq_to_desc(irqnr);
                                         desc->handle_irq(irqnr, desc);
                                         if (asic->irq_bothedge[bank] & bit)
                                                 asic3_irq_flip_edge(asic, base,
@@ -136,7 +136,7 @@ static void asic3_irq_demux(unsigned int irq, struct irq_desc *desc)
                 for (i = ASIC3_NUM_GPIOS; i < ASIC3_NR_IRQS; i++) {
                         /* They start at bit 4 and go up */
                         if (status & (1 << (i - ASIC3_NUM_GPIOS + 4))) {
-                                desc = irq_desc + asic->irq_base + i;
+                                desc = irq_to_desc(asic->irq_base + i);
                                 desc->handle_irq(asic->irq_base + i,
                                                  desc);
                         }
diff --git a/drivers/mfd/htc-egpio.c b/drivers/mfd/htc-egpio.c
index 6be43172dc65..ad3379fcd194 100644
--- a/drivers/mfd/htc-egpio.c
+++ b/drivers/mfd/htc-egpio.c
@@ -112,7 +112,7 @@ static void egpio_handler(unsigned int irq, struct irq_desc *desc)
                 /* Run irq handler */
                 pr_debug("got IRQ %d\n", irqpin);
                 irq = ei->irq_start + irqpin;
-                desc = &irq_desc[irq];
+                desc = irq_to_desc(irq);
                 desc->handle_irq(irq, desc);
         }
 }
diff --git a/drivers/parisc/dino.c b/drivers/parisc/dino.c
index fd56128525d1..3bc54b30c3a1 100644
--- a/drivers/parisc/dino.c
+++ b/drivers/parisc/dino.c
@@ -298,7 +298,8 @@ struct pci_port_ops dino_port_ops = {
 
 static void dino_disable_irq(unsigned int irq)
 {
-        struct dino_device *dino_dev = irq_desc[irq].chip_data;
+        struct irq_desc *desc = irq_to_desc(irq);
+        struct dino_device *dino_dev = desc->chip_data;
         int local_irq = gsc_find_local_irq(irq, dino_dev->global_irq, DINO_LOCAL_IRQS);
 
         DBG(KERN_WARNING "%s(0x%p, %d)\n", __func__, dino_dev, irq);
@@ -310,7 +311,8 @@ static void dino_disable_irq(unsigned int irq)
 
 static void dino_enable_irq(unsigned int irq)
 {
-        struct dino_device *dino_dev = irq_desc[irq].chip_data;
+        struct irq_desc *desc = irq_to_desc(irq);
+        struct dino_device *dino_dev = desc->chip_data;
         int local_irq = gsc_find_local_irq(irq, dino_dev->global_irq, DINO_LOCAL_IRQS);
         u32 tmp;
 
diff --git a/drivers/parisc/eisa.c b/drivers/parisc/eisa.c
index 771cef592542..7891db50c483 100644
--- a/drivers/parisc/eisa.c
+++ b/drivers/parisc/eisa.c
@@ -346,10 +346,10 @@ static int __init eisa_probe(struct parisc_device *dev)
         }
         
         /* Reserve IRQ2 */
-        irq_desc[2].action = &irq2_action;
+        irq_to_desc(2)->action = &irq2_action;
         
         for (i = 0; i < 16; i++) {
-                irq_desc[i].chip = &eisa_interrupt_type;
+                irq_to_desc(i)->chip = &eisa_interrupt_type;
         }
         
         EISA_bus = 1;
diff --git a/drivers/parisc/gsc.c b/drivers/parisc/gsc.c
index f7d088b897ee..e76db9e4d504 100644
--- a/drivers/parisc/gsc.c
+++ b/drivers/parisc/gsc.c
@@ -108,7 +108,8 @@ int gsc_find_local_irq(unsigned int irq, int *global_irqs, int limit)
 
 static void gsc_asic_disable_irq(unsigned int irq)
 {
-        struct gsc_asic *irq_dev = irq_desc[irq].chip_data;
+        struct irq_desc *desc = irq_to_desc(irq);
+        struct gsc_asic *irq_dev = desc->chip_data;
         int local_irq = gsc_find_local_irq(irq, irq_dev->global_irq, 32);
         u32 imr;
 
@@ -123,7 +124,8 @@ static void gsc_asic_disable_irq(unsigned int irq)
 
 static void gsc_asic_enable_irq(unsigned int irq)
 {
-        struct gsc_asic *irq_dev = irq_desc[irq].chip_data;
+        struct irq_desc *desc = irq_to_desc(irq);
+        struct gsc_asic *irq_dev = desc->chip_data;
         int local_irq = gsc_find_local_irq(irq, irq_dev->global_irq, 32);
         u32 imr;
 
@@ -159,12 +161,14 @@ static struct hw_interrupt_type gsc_asic_interrupt_type = {
 int gsc_assign_irq(struct hw_interrupt_type *type, void *data)
 {
         static int irq = GSC_IRQ_BASE;
+        struct irq_desc *desc;
 
         if (irq > GSC_IRQ_MAX)
                 return NO_IRQ;
 
-        irq_desc[irq].chip = type;
-        irq_desc[irq].chip_data = data;
+        desc = irq_to_desc(irq);
+        desc->chip = type;
+        desc->chip_data = data;
         return irq++;
 }
 
diff --git a/drivers/parisc/iosapic.c b/drivers/parisc/iosapic.c
index 6fb3f7979f21..7beffcab2745 100644
--- a/drivers/parisc/iosapic.c
+++ b/drivers/parisc/iosapic.c
@@ -619,7 +619,9 @@ iosapic_set_irt_data( struct vector_info *vi, u32 *dp0, u32 *dp1)
 
 static struct vector_info *iosapic_get_vector(unsigned int irq)
 {
-        return irq_desc[irq].chip_data;
+        struct irq_desc *desc = irq_to_desc(irq);
+
+        return desc->chip_data;
 }
 
 static void iosapic_disable_irq(unsigned int irq)
diff --git a/drivers/parisc/superio.c b/drivers/parisc/superio.c
index 1e8d2d17f04c..1e93c837514f 100644
--- a/drivers/parisc/superio.c
+++ b/drivers/parisc/superio.c
@@ -363,7 +363,9 @@ int superio_fixup_irq(struct pci_dev *pcidev)
 #endif
 
         for (i = 0; i < 16; i++) {
-                irq_desc[i].chip = &superio_interrupt_type;
+                struct irq_desc *desc = irq_to_desc(i);
+
+                desc->chip = &superio_interrupt_type;
         }
 
         /*
diff --git a/drivers/pcmcia/hd64465_ss.c b/drivers/pcmcia/hd64465_ss.c
index 117dc12ab438..9ef69cdb3183 100644
--- a/drivers/pcmcia/hd64465_ss.c
+++ b/drivers/pcmcia/hd64465_ss.c
@@ -233,15 +233,18 @@ static struct hw_interrupt_type hd64465_ss_irq_type = {
  */
 static void hs_map_irq(hs_socket_t *sp, unsigned int irq)
 {
+        struct irq_desc *desc;
+
         DPRINTK("hs_map_irq(sock=%d irq=%d)\n", sp->number, irq);
         
         if (irq >= HS_NUM_MAPPED_IRQS)
             return;
 
+        desc = irq_to_desc(irq);
         hs_mapped_irq[irq].sock = sp;
         /* insert ourselves as the irq controller */
-        hs_mapped_irq[irq].old_handler = irq_desc[irq].chip;
-        irq_desc[irq].chip = &hd64465_ss_irq_type;
+        hs_mapped_irq[irq].old_handler = desc->chip;
+        desc->chip = &hd64465_ss_irq_type;
 }
 
 
@@ -250,13 +253,16 @@ static void hs_map_irq(hs_socket_t *sp, unsigned int irq)
  */
 static void hs_unmap_irq(hs_socket_t *sp, unsigned int irq)
 {
+        struct irq_desc *desc;
+
         DPRINTK("hs_unmap_irq(sock=%d irq=%d)\n", sp->number, irq);
         
         if (irq >= HS_NUM_MAPPED_IRQS)
             return;
                 
+        desc = irq_to_desc(irq);
         /* restore the original irq controller */
-        irq_desc[irq].chip = hs_mapped_irq[irq].old_handler;
+        desc->chip = hs_mapped_irq[irq].old_handler;
 }
 
 /*============================================================*/
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index ed8235187dc0..56ace47f24d6 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -125,7 +125,7 @@ static void bind_evtchn_to_cpu(unsigned int chn, unsigned int cpu)
 
         BUG_ON(irq == -1);
 #ifdef CONFIG_SMP
-        irq_desc[irq].affinity = cpumask_of_cpu(cpu);
+        irq_to_desc(irq)->affinity = cpumask_of_cpu(cpu);
 #endif
 
         __clear_bit(chn, cpu_evtchn_mask[cpu_evtchn[chn]]);
@@ -139,8 +139,10 @@ static void init_evtchn_cpu_bindings(void)
 #ifdef CONFIG_SMP
         int i;
         /* By default all event channels notify CPU#0. */
-        for (i = 0; i < nr_irqs; i++)
-                irq_desc[i].affinity = cpumask_of_cpu(0);
+        for (i = 0; i < nr_irqs; i++) {
+                struct irq_desc *desc = irq_to_desc(i);
+                desc->affinity = cpumask_of_cpu(0);
+        }
 #endif
 
         memset(cpu_evtchn, 0, sizeof(cpu_evtchn));
diff --git a/include/linux/irq.h b/include/linux/irq.h
index 5f4b013624dc..80b8200f2adb 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -152,6 +152,10 @@ struct irq_chip {
  * @name:               flow handler name for /proc/interrupts output
  */
 struct irq_desc {
+        unsigned int            irq;
+#ifdef CONFIG_HAVE_SPARSE_IRQ
+        struct irq_desc         *next;
+#endif
         irq_flow_handler_t      handle_irq;
         struct irq_chip         *chip;
         struct msi_desc         *msi_desc;
@@ -179,9 +183,9 @@ struct irq_desc {
         const char              *name;
 } ____cacheline_internodealigned_in_smp;
 
-#ifdef CONFIG_HAVE_DYN_ARRAY
-extern struct irq_desc *irq_desc;
-#else
+extern struct irq_desc *irq_to_desc(unsigned int irq);
+#ifndef CONFIG_HAVE_DYN_ARRAY
+/* could be removed if we get rid of all irq_desc reference */
 extern struct irq_desc irq_desc[NR_IRQS];
 #endif
 
@@ -249,7 +253,10 @@ extern int no_irq_affinity;
 
 static inline int irq_balancing_disabled(unsigned int irq)
 {
-        return irq_desc[irq].status & IRQ_NO_BALANCING_MASK;
+        struct irq_desc *desc;
+
+        desc = irq_to_desc(irq);
+        return desc->status & IRQ_NO_BALANCING_MASK;
 }
 
 /* Handle irq action chains: */
@@ -281,7 +288,7 @@ extern unsigned int __do_IRQ(unsigned int irq);
  */
 static inline void generic_handle_irq(unsigned int irq)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
 
 #ifdef CONFIG_GENERIC_HARDIRQS_NO__DO_IRQ
         desc->handle_irq(irq, desc);
@@ -325,7 +332,10 @@ __set_irq_handler(unsigned int irq, irq_flow_handler_t handle, int is_chained,
 static inline void __set_irq_handler_unlocked(int irq,
                                               irq_flow_handler_t handler)
 {
-        irq_desc[irq].handle_irq = handler;
+        struct irq_desc *desc;
+
+        desc = irq_to_desc(irq);
+        desc->handle_irq = handler;
 }
 
 /*
@@ -359,7 +369,7 @@ extern void destroy_irq(unsigned int irq);
 /* Test to see if a driver has successfully requested an irq */
 static inline int irq_has_action(unsigned int irq)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
         return desc->action != NULL;
 }
 
@@ -374,10 +384,10 @@ extern int set_irq_chip_data(unsigned int irq, void *data);
 extern int set_irq_type(unsigned int irq, unsigned int type);
 extern int set_irq_msi(unsigned int irq, struct msi_desc *entry);
 
-#define get_irq_chip(irq)       (irq_desc[irq].chip)
-#define get_irq_chip_data(irq)  (irq_desc[irq].chip_data)
-#define get_irq_data(irq)       (irq_desc[irq].handler_data)
-#define get_irq_msi(irq)        (irq_desc[irq].msi_desc)
+#define get_irq_chip(irq)       (irq_to_desc(irq)->chip)
+#define get_irq_chip_data(irq)  (irq_to_desc(irq)->chip_data)
+#define get_irq_data(irq)       (irq_to_desc(irq)->handler_data)
+#define get_irq_msi(irq)        (irq_to_desc(irq)->msi_desc)
 
 #endif /* CONFIG_GENERIC_HARDIRQS */
 
diff --git a/kernel/irq/autoprobe.c b/kernel/irq/autoprobe.c
index c689e9851a80..c45ab718cf07 100644
--- a/kernel/irq/autoprobe.c
+++ b/kernel/irq/autoprobe.c
@@ -39,7 +39,7 @@ unsigned long probe_irq_on(void)
          * flush such a longstanding irq before considering it as spurious.
          */
         for (i = nr_irqs-1; i > 0; i--) {
-                desc = irq_desc + i;
+                desc = irq_to_desc(i);
 
                 spin_lock_irq(&desc->lock);
                 if (!desc->action && !(desc->status & IRQ_NOPROBE)) {
@@ -69,7 +69,7 @@ unsigned long probe_irq_on(void)
          * happened in the previous stage, it may have masked itself)
          */
         for (i = nr_irqs-1; i > 0; i--) {
-                desc = irq_desc + i;
+                desc = irq_to_desc(i);
 
                 spin_lock_irq(&desc->lock);
                 if (!desc->action && !(desc->status & IRQ_NOPROBE)) {
@@ -92,7 +92,7 @@ unsigned long probe_irq_on(void)
         for (i = 0; i < nr_irqs; i++) {
                 unsigned int status;
 
-                desc = irq_desc + i;
+                desc = irq_to_desc(i);
                 spin_lock_irq(&desc->lock);
                 status = desc->status;
 
@@ -131,7 +131,7 @@ unsigned int probe_irq_mask(unsigned long val)
 
         mask = 0;
         for (i = 0; i < nr_irqs; i++) {
-                struct irq_desc *desc = irq_desc + i;
+                struct irq_desc *desc = irq_to_desc(i);
                 unsigned int status;
 
                 spin_lock_irq(&desc->lock);
@@ -174,7 +174,7 @@ int probe_irq_off(unsigned long val)
         int i, irq_found = 0, nr_irqs = 0;
 
         for (i = 0; i < nr_irqs; i++) {
-                struct irq_desc *desc = irq_desc + i;
+                struct irq_desc *desc = irq_to_desc(i);
                 unsigned int status;
 
                 spin_lock_irq(&desc->lock);
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index bba66e098703..76c225cf4b26 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -33,7 +33,7 @@ void dynamic_irq_init(unsigned int irq)
         }
 
         /* Ensure we don't have left over values from a previous use of this irq */
-        desc = irq_desc + irq;
+        desc = irq_to_desc(irq);
         spin_lock_irqsave(&desc->lock, flags);
         desc->status = IRQ_DISABLED;
         desc->chip = &no_irq_chip;
@@ -65,7 +65,7 @@ void dynamic_irq_cleanup(unsigned int irq)
                 return;
         }
 
-        desc = irq_desc + irq;
+        desc = irq_to_desc(irq);
         spin_lock_irqsave(&desc->lock, flags);
         if (desc->action) {
                 spin_unlock_irqrestore(&desc->lock, flags);
@@ -100,7 +100,7 @@ int set_irq_chip(unsigned int irq, struct irq_chip *chip)
         if (!chip)
                 chip = &no_irq_chip;
 
-        desc = irq_desc + irq;
+        desc = irq_to_desc(irq);
         spin_lock_irqsave(&desc->lock, flags);
         irq_chip_set_defaults(chip);
         desc->chip = chip;
@@ -126,7 +126,7 @@ int set_irq_type(unsigned int irq, unsigned int type)
                 return -ENODEV;
         }
 
-        desc = irq_desc + irq;
+        desc = irq_to_desc(irq);
         if (type == IRQ_TYPE_NONE)
                 return 0;
 
@@ -155,7 +155,7 @@ int set_irq_data(unsigned int irq, void *data)
                 return -EINVAL;
         }
 
-        desc = irq_desc + irq;
+        desc = irq_to_desc(irq);
         spin_lock_irqsave(&desc->lock, flags);
         desc->handler_data = data;
         spin_unlock_irqrestore(&desc->lock, flags);
@@ -180,7 +180,7 @@ int set_irq_msi(unsigned int irq, struct msi_desc *entry)
                        "Trying to install msi data for IRQ%d\n", irq);
                 return -EINVAL;
         }
-        desc = irq_desc + irq;
+        desc = irq_to_desc(irq);
         spin_lock_irqsave(&desc->lock, flags);
         desc->msi_desc = entry;
         if (entry)
@@ -198,9 +198,10 @@ int set_irq_msi(unsigned int irq, struct msi_desc *entry)
  */
 int set_irq_chip_data(unsigned int irq, void *data)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc;
         unsigned long flags;
 
+        desc = irq_to_desc(irq);
         if (irq >= nr_irqs || !desc->chip) {
                 printk(KERN_ERR "BUG: bad set_irq_chip_data(IRQ#%d)\n", irq);
                 return -EINVAL;
@@ -219,8 +220,9 @@ EXPORT_SYMBOL(set_irq_chip_data);
  */
 static void default_enable(unsigned int irq)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc;
 
+        desc = irq_to_desc(irq);
         desc->chip->unmask(irq);
         desc->status &= ~IRQ_MASKED;
 }
@@ -237,7 +239,10 @@ static void default_disable(unsigned int irq)
  */
 static unsigned int default_startup(unsigned int irq)
 {
-        irq_desc[irq].chip->enable(irq);
+        struct irq_desc *desc;
+
+        desc = irq_to_desc(irq);
+        desc->chip->enable(irq);
 
         return 0;
 }
@@ -247,8 +252,9 @@ static unsigned int default_startup(unsigned int irq)
  */
 static void default_shutdown(unsigned int irq)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc;
 
+        desc = irq_to_desc(irq);
         desc->chip->mask(irq);
         desc->status |= IRQ_MASKED;
 }
@@ -551,7 +557,7 @@ __set_irq_handler(unsigned int irq, irq_flow_handler_t handle, int is_chained,
                 return;
         }
 
-        desc = irq_desc + irq;
+        desc = irq_to_desc(irq);
 
         if (!handle)
                 handle = handle_bad_irq;
@@ -616,7 +622,7 @@ void __init set_irq_noprobe(unsigned int irq)
                 return;
         }
 
-        desc = irq_desc + irq;
+        desc = irq_to_desc(irq);
 
         spin_lock_irqsave(&desc->lock, flags);
         desc->status |= IRQ_NOPROBE;
@@ -634,7 +640,7 @@ void __init set_irq_probe(unsigned int irq)
                 return;
         }
 
-        desc = irq_desc + irq;
+        desc = irq_to_desc(irq);
 
         spin_lock_irqsave(&desc->lock, flags);
         desc->status &= ~IRQ_NOPROBE;
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index 6ce3bcc2b8f7..9fc33b3378e6 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -18,6 +18,14 @@
 
 #include "internals.h"
 
+#ifdef CONFIG_TRACE_IRQFLAGS
+
+/*
+ * lockdep: we want to handle all irq_desc locks as a single lock-class:
+ */
+static struct lock_class_key irq_desc_lock_class;
+#endif
+
 /**
  * handle_bad_irq - handle spurious and unhandled irqs
  * @irq:       the interrupt number
@@ -51,7 +59,8 @@ int nr_irqs = NR_IRQS;
 EXPORT_SYMBOL_GPL(nr_irqs);
 
 #ifdef CONFIG_HAVE_DYN_ARRAY
-static struct irq_desc irq_desc_init __initdata = {
+static struct irq_desc irq_desc_init = {
+        .irq = -1U,
         .status = IRQ_DISABLED,
         .chip = &no_irq_chip,
         .handle_irq = handle_bad_irq,
@@ -62,6 +71,27 @@ static struct irq_desc irq_desc_init __initdata = {
 #endif
 };
 
+
+static void init_one_irq_desc(struct irq_desc *desc)
+{
+        memcpy(desc, &irq_desc_init, sizeof(struct irq_desc));
+#ifdef CONFIG_TRACE_IRQFLAGS
+        lockdep_set_class(&desc->lock, &irq_desc_lock_class);
+#endif
+}
+
+#ifdef CONFIG_HAVE_SPARSE_IRQ
+static int nr_irq_desc = 32;
+
+static int __init parse_nr_irq_desc(char *arg)
+{
+        if (arg)
+                nr_irq_desc = simple_strtoul(arg, NULL, 0);
+        return 0;
+}
+
+early_param("nr_irq_desc", parse_nr_irq_desc);
+
 static void __init init_work(void *data)
 {
         struct dyn_array *da = data;
@@ -71,12 +101,83 @@ static void __init init_work(void *data)
         desc = *da->name;
 
         for (i = 0; i < *da->nr; i++)
-                memcpy(&desc[i], &irq_desc_init, sizeof(struct irq_desc));
+                init_one_irq_desc(&desc[i]);
+
+        for (i = 1; i < *da->nr; i++)
+                desc[i-1].next = &desc[i];
 }
 
-struct irq_desc *irq_desc;
+static struct irq_desc *sparse_irqs;
+DEFINE_DYN_ARRAY(sparse_irqs, sizeof(struct irq_desc), nr_irq_desc, PAGE_SIZE, init_work);
+
+extern int after_bootmem;
+extern void *__alloc_bootmem_nopanic(unsigned long size,
+                             unsigned long align,
+                             unsigned long goal);
+struct irq_desc *irq_to_desc(unsigned int irq)
+{
+        struct irq_desc *desc, *desc_pri;
+        int i;
+        int count = 0;
+
+        BUG_ON(irq == -1U);
+
+        desc_pri = desc = &sparse_irqs[0];
+        while (desc) {
+                if (desc->irq == irq)
+                        return desc;
+
+                if (desc->irq == -1U) {
+                        desc->irq = irq;
+                        return desc;
+                }
+                desc_pri = desc;
+                desc = desc->next;
+                count++;
+        }
+
+        /*
+         *  we run out of pre-allocate ones, allocate more
+         */
+        printk(KERN_DEBUG "try to get more irq_desc %d\n", nr_irq_desc);
+
+        if (after_bootmem)
+                desc = kzalloc(sizeof(struct irq_desc)*nr_irq_desc, GFP_ATOMIC);
+        else
+                desc = __alloc_bootmem_nopanic(sizeof(struct irq_desc)*nr_irq_desc, PAGE_SIZE, 0);
+
+        if (!desc)
+                panic("please boot with nr_irq_desc= %d\n", count * 2);
+
+        for (i = 0; i < nr_irq_desc; i++)
+                init_one_irq_desc(&desc[i]);
+
+        for (i = 1; i < nr_irq_desc; i++)
+                desc[i-1].next = &desc[i];
+
+        desc->irq = irq;
+        desc_pri->next = desc;
+
+        return desc;
+}
+#else
+static void __init init_work(void *data)
+{
+        struct dyn_array *da = data;
+        int i;
+        struct  irq_desc *desc;
+
+        desc = *da->name;
+
+        for (i = 0; i < *da->nr; i++)
+                init_one_irq_desc(&desc[i]);
+
+}
+static struct irq_desc *irq_desc;
 DEFINE_DYN_ARRAY(irq_desc, sizeof(struct irq_desc), nr_irqs, PAGE_SIZE, init_work);
 
+#endif
+
 #else
 
 struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
@@ -85,12 +186,23 @@ struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
                 .chip = &no_irq_chip,
                 .handle_irq = handle_bad_irq,
                 .depth = 1,
-                .lock = __SPIN_LOCK_UNLOCKED(irq_desc->lock),
+                .lock = __SPIN_LOCK_UNLOCKED(sparse_irqs->lock),
 #ifdef CONFIG_SMP
                 .affinity = CPU_MASK_ALL
 #endif
         }
 };
+
+#endif
+
+#ifndef CONFIG_HAVE_SPARSE_IRQ
+struct irq_desc *irq_to_desc(unsigned int irq)
+{
+        if (irq < nr_irqs)
+                return &irq_desc[irq];
+
+        return NULL;
+}
 #endif
 
 /*
@@ -99,7 +211,10 @@ struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
  */
 static void ack_bad(unsigned int irq)
 {
-        print_irq_desc(irq, irq_desc + irq);
+        struct irq_desc *desc;
+
+        desc = irq_to_desc(irq);
+        print_irq_desc(irq, desc);
         ack_bad_irq(irq);
 }
 
@@ -196,7 +311,7 @@ irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action)
  */
 unsigned int __do_IRQ(unsigned int irq)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
         struct irqaction *action;
         unsigned int status;
 
@@ -287,19 +402,16 @@ out:
 }
 #endif
 
-#ifdef CONFIG_TRACE_IRQFLAGS
-
-/*
- * lockdep: we want to handle all irq_desc locks as a single lock-class:
- */
-static struct lock_class_key irq_desc_lock_class;
 
+#ifdef CONFIG_TRACE_IRQFLAGS
 void early_init_irq_lock_class(void)
 {
+#ifndef CONFIG_HAVE_DYN_ARRAY
         int i;
 
         for (i = 0; i < nr_irqs; i++)
                 lockdep_set_class(&irq_desc[i].lock, &irq_desc_lock_class);
+#endif
 }
-
 #endif
+
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index d5a4333d8f1f..b5943e9f95aa 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -31,7 +31,7 @@ cpumask_t irq_default_affinity = CPU_MASK_ALL;
  */
 void synchronize_irq(unsigned int irq)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
         unsigned int status;
 
         if (irq >= nr_irqs)
@@ -64,7 +64,7 @@ EXPORT_SYMBOL(synchronize_irq);
  */
 int irq_can_set_affinity(unsigned int irq)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
 
         if (CHECK_IRQ_PER_CPU(desc->status) || !desc->chip ||
             !desc->chip->set_affinity)
@@ -81,7 +81,7 @@ int irq_can_set_affinity(unsigned int irq)
  */
 int irq_set_affinity(unsigned int irq, cpumask_t cpumask)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
 
         if (!desc->chip->set_affinity)
                 return -EINVAL;
@@ -111,14 +111,16 @@ int irq_set_affinity(unsigned int irq, cpumask_t cpumask)
 int irq_select_affinity(unsigned int irq)
 {
         cpumask_t mask;
+        struct irq_desc *desc;
 
         if (!irq_can_set_affinity(irq))
                 return 0;
 
         cpus_and(mask, cpu_online_map, irq_default_affinity);
 
-        irq_desc[irq].affinity = mask;
-        irq_desc[irq].chip->set_affinity(irq, mask);
+        desc = irq_to_desc(irq);
+        desc->affinity = mask;
+        desc->chip->set_affinity(irq, mask);
 
         set_balance_irq_affinity(irq, mask);
         return 0;
@@ -140,7 +142,7 @@ int irq_select_affinity(unsigned int irq)
  */
 void disable_irq_nosync(unsigned int irq)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
         unsigned long flags;
 
         if (irq >= nr_irqs)
@@ -169,7 +171,7 @@ EXPORT_SYMBOL(disable_irq_nosync);
  */
 void disable_irq(unsigned int irq)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
 
         if (irq >= nr_irqs)
                 return;
@@ -211,7 +213,7 @@ static void __enable_irq(struct irq_desc *desc, unsigned int irq)
  */
 void enable_irq(unsigned int irq)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
         unsigned long flags;
 
         if (irq >= nr_irqs)
@@ -225,7 +227,7 @@ EXPORT_SYMBOL(enable_irq);
 
 static int set_irq_wake_real(unsigned int irq, unsigned int on)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
         int ret = -ENXIO;
 
         if (desc->chip->set_wake)
@@ -248,7 +250,7 @@ static int set_irq_wake_real(unsigned int irq, unsigned int on)
  */
 int set_irq_wake(unsigned int irq, unsigned int on)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
         unsigned long flags;
         int ret = 0;
 
@@ -288,12 +290,13 @@ EXPORT_SYMBOL(set_irq_wake);
  */
 int can_request_irq(unsigned int irq, unsigned long irqflags)
 {
+        struct irq_desc *desc = irq_to_desc(irq);
         struct irqaction *action;
 
-        if (irq >= nr_irqs || irq_desc[irq].status & IRQ_NOREQUEST)
+        if (irq >= nr_irqs || desc->status & IRQ_NOREQUEST)
                 return 0;
 
-        action = irq_desc[irq].action;
+        action = desc->action;
         if (action)
                 if (irqflags & action->flags & IRQF_SHARED)
                         action = NULL;
@@ -349,7 +352,7 @@ int __irq_set_trigger(struct irq_desc *desc, unsigned int irq,
  */
 int setup_irq(unsigned int irq, struct irqaction *new)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
         struct irqaction *old, **p;
         const char *old_name = NULL;
         unsigned long flags;
@@ -518,7 +521,7 @@ void free_irq(unsigned int irq, void *dev_id)
         if (irq >= nr_irqs)
                 return;
 
-        desc = irq_desc + irq;
+        desc = irq_to_desc(irq);
         spin_lock_irqsave(&desc->lock, flags);
         p = &desc->action;
         for (;;) {
@@ -615,6 +618,7 @@ int request_irq(unsigned int irq, irq_handler_t handler,
 {
         struct irqaction *action;
         int retval;
+        struct irq_desc *desc;
 
 #ifdef CONFIG_LOCKDEP
         /*
@@ -632,7 +636,8 @@ int request_irq(unsigned int irq, irq_handler_t handler,
                 return -EINVAL;
         if (irq >= nr_irqs)
                 return -EINVAL;
-        if (irq_desc[irq].status & IRQ_NOREQUEST)
+        desc = irq_to_desc(irq);
+        if (desc->status & IRQ_NOREQUEST)
                 return -EINVAL;
         if (!handler)
                 return -EINVAL;
diff --git a/kernel/irq/migration.c b/kernel/irq/migration.c
index 77b7acc875c5..90b920d3f52b 100644
--- a/kernel/irq/migration.c
+++ b/kernel/irq/migration.c
@@ -3,18 +3,18 @@
 
 void set_pending_irq(unsigned int irq, cpumask_t mask)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
         unsigned long flags;
 
         spin_lock_irqsave(&desc->lock, flags);
         desc->status |= IRQ_MOVE_PENDING;
-        irq_desc[irq].pending_mask = mask;
+        desc->pending_mask = mask;
         spin_unlock_irqrestore(&desc->lock, flags);
 }
 
 void move_masked_irq(int irq)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
         cpumask_t tmp;
 
         if (likely(!(desc->status & IRQ_MOVE_PENDING)))
@@ -30,7 +30,7 @@ void move_masked_irq(int irq)
 
         desc->status &= ~IRQ_MOVE_PENDING;
 
-        if (unlikely(cpus_empty(irq_desc[irq].pending_mask)))
+        if (unlikely(cpus_empty(desc->pending_mask)))
                 return;
 
         if (!desc->chip->set_affinity)
@@ -38,7 +38,7 @@ void move_masked_irq(int irq)
 
         assert_spin_locked(&desc->lock);
 
-        cpus_and(tmp, irq_desc[irq].pending_mask, cpu_online_map);
+        cpus_and(tmp, desc->pending_mask, cpu_online_map);
 
         /*
          * If there was a valid mask to work with, please
@@ -55,12 +55,12 @@ void move_masked_irq(int irq)
         if (likely(!cpus_empty(tmp))) {
                 desc->chip->set_affinity(irq,tmp);
         }
-        cpus_clear(irq_desc[irq].pending_mask);
+        cpus_clear(desc->pending_mask);
 }
 
 void move_native_irq(int irq)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
 
         if (likely(!(desc->status & IRQ_MOVE_PENDING)))
                 return;
diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index e5225a65a4f9..c2f356c808f6 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -19,7 +19,7 @@ static struct proc_dir_entry *root_irq_dir;
 
 static int irq_affinity_proc_show(struct seq_file *m, void *v)
 {
-        struct irq_desc *desc = irq_desc + (long)m->private;
+        struct irq_desc *desc = irq_to_desc((long)m->private);
         cpumask_t *mask = &desc->affinity;
 
 #ifdef CONFIG_GENERIC_PENDING_IRQ
@@ -43,7 +43,7 @@ static ssize_t irq_affinity_proc_write(struct file *file,
         cpumask_t new_value;
         int err;
 
-        if (!irq_desc[irq].chip->set_affinity || no_irq_affinity ||
+        if (!irq_to_desc(irq)->chip->set_affinity || no_irq_affinity ||
             irq_balancing_disabled(irq))
                 return -EIO;
 
@@ -132,20 +132,20 @@ static const struct file_operations default_affinity_proc_fops = {
 static int irq_spurious_read(char *page, char **start, off_t off,
                                   int count, int *eof, void *data)
 {
-        struct irq_desc *d = &irq_desc[(long) data];
+        struct irq_desc *desc = irq_to_desc((long) data);
         return sprintf(page, "count %u\n"
                              "unhandled %u\n"
                              "last_unhandled %u ms\n",
-                        d->irq_count,
-                        d->irqs_unhandled,
-                        jiffies_to_msecs(d->last_unhandled));
+                        desc->irq_count,
+                        desc->irqs_unhandled,
+                        jiffies_to_msecs(desc->last_unhandled));
 }
 
 #define MAX_NAMELEN 128
 
 static int name_unique(unsigned int irq, struct irqaction *new_action)
 {
-        struct irq_desc *desc = irq_desc + irq;
+        struct irq_desc *desc = irq_to_desc(irq);
         struct irqaction *action;
         unsigned long flags;
         int ret = 1;
@@ -165,8 +165,9 @@ static int name_unique(unsigned int irq, struct irqaction *new_action)
 void register_handler_proc(unsigned int irq, struct irqaction *action)
 {
         char name [MAX_NAMELEN];
+        struct irq_desc *desc = irq_to_desc(irq);
 
-        if (!irq_desc[irq].dir || action->dir || !action->name ||
+        if (!desc->dir || action->dir || !action->name ||
                                         !name_unique(irq, action))
                 return;
 
@@ -174,7 +175,7 @@ void register_handler_proc(unsigned int irq, struct irqaction *action)
         snprintf(name, MAX_NAMELEN, "%s", action->name);
 
         /* create /proc/irq/1234/handler/ */
-        action->dir = proc_mkdir(name, irq_desc[irq].dir);
+        action->dir = proc_mkdir(name, desc->dir);
 }
 
 #undef MAX_NAMELEN
@@ -185,25 +186,24 @@ void register_irq_proc(unsigned int irq)
 {
         char name [MAX_NAMELEN];
         struct proc_dir_entry *entry;
+        struct irq_desc *desc = irq_to_desc(irq);
 
-        if (!root_irq_dir ||
-                (irq_desc[irq].chip == &no_irq_chip) ||
-                        irq_desc[irq].dir)
+        if (!root_irq_dir || (desc->chip == &no_irq_chip) || desc->dir)
                 return;
 
         memset(name, 0, MAX_NAMELEN);
         sprintf(name, "%d", irq);
 
         /* create /proc/irq/1234 */
-        irq_desc[irq].dir = proc_mkdir(name, root_irq_dir);
+        desc->dir = proc_mkdir(name, root_irq_dir);
 
 #ifdef CONFIG_SMP
         /* create /proc/irq/<irq>/smp_affinity */
-        proc_create_data("smp_affinity", 0600, irq_desc[irq].dir,
+        proc_create_data("smp_affinity", 0600, desc->dir,
                          &irq_affinity_proc_fops, (void *)(long)irq);
 #endif
 
-        entry = create_proc_entry("spurious", 0444, irq_desc[irq].dir);
+        entry = create_proc_entry("spurious", 0444, desc->dir);
         if (entry) {
                 entry->data = (void *)(long)irq;
                 entry->read_proc = irq_spurious_read;
@@ -214,8 +214,10 @@ void register_irq_proc(unsigned int irq)
 
 void unregister_handler_proc(unsigned int irq, struct irqaction *action)
 {
-        if (action->dir)
-                remove_proc_entry(action->dir->name, irq_desc[irq].dir);
+        if (action->dir) {
+                struct irq_desc *desc = irq_to_desc(irq);
+                remove_proc_entry(action->dir->name, desc->dir);
+        }
 }
 
 void register_default_affinity_proc(void)
diff --git a/kernel/irq/resend.c b/kernel/irq/resend.c
index cba8aa5bc7f4..89c7117acf2b 100644
--- a/kernel/irq/resend.c
+++ b/kernel/irq/resend.c
@@ -36,7 +36,7 @@ static void resend_irqs(unsigned long arg)
         while (!bitmap_empty(irqs_resend, nr_irqs)) {
                 irq = find_first_bit(irqs_resend, nr_irqs);
                 clear_bit(irq, irqs_resend);
-                desc = irq_desc + irq;
+                desc = irq_to_desc(irq);
                 local_irq_disable();
                 desc->handle_irq(irq, desc);
                 local_irq_enable();
diff --git a/kernel/irq/spurious.c b/kernel/irq/spurious.c
index e26ca1e90c08..b5d906002e1d 100644
--- a/kernel/irq/spurious.c
+++ b/kernel/irq/spurious.c
@@ -92,11 +92,12 @@ static int misrouted_irq(int irq)
         int ok = 0;
 
         for (i = 1; i < nr_irqs; i++) {
-                struct irq_desc *desc = irq_desc + i;
+                struct irq_desc *desc;
 
                 if (i == irq)   /* Already tried */
                         continue;
 
+                desc = irq_to_desc(i);
                 if (try_one_irq(i, desc))
                         ok = 1;
         }
@@ -108,7 +109,7 @@ static void poll_spurious_irqs(unsigned long dummy)
 {
         int i;
         for (i = 1; i < nr_irqs; i++) {
-                struct irq_desc *desc = irq_desc + i;
+                struct irq_desc *desc = irq_to_desc(i);
                 unsigned int status;
 
                 /* Racy but it doesn't matter */