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, 199 insertions, 73 deletions

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 */