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>

1 files changed, 6 insertions, 4 deletions

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;
                 }
         }
 }