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>

8 files changed, 142 insertions, 83 deletions

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);
 	{