ARM: 6532/1: Allow machine to specify it's own IRQ handlers at run-time

Normally different ARM platform has different way to decode the IRQ
hardware status and demultiplex to the corresponding IRQ handler.
This is highly optimized by macro irq_handler in entry-armv.S, and
each machine defines their own macro to decode the IRQ number.
However, this prevents multiple machine classes to be built into a
single kernel.

By allowing each machine to specify thier own handler, and making
function pointer 'handle_arch_irq' to point to it at run time, this
can be solved. And introduce CONFIG_MULTI_IRQ_HANDLER to allow both
solutions to work.

Comparing with the highly optimized macro of irq_handler, the new
function must be written with care not to lose too much performance.
And the IPI stuff on SMP is expected to move to the provided arch
IRQ handler as well.

The assembly code to invoke handle_arch_irq is optimized by Russell
King.

Signed-off-by: Eric Miao <eric.miao@canonical.com>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 15 insertions, 2 deletions

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 35f3f20d6731..caa6c396ec78 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -30,6 +30,14 @@
  * Interrupt handling.  Preserves r7, r8, r9
  */
         .macro  irq_handler
+#ifdef CONFIG_MULTI_IRQ_HANDLER
+        ldr     r5, =handle_arch_irq
+        mov     r0, sp
+        ldr     r5, [r5]
+        adr     lr, BSYM(9997f)
+        teq     r5, #0
+        movne   pc, r5
+#endif
         get_irqnr_preamble r5, lr
 1:      get_irqnr_and_base r0, r6, r5, lr
         movne   r1, sp
@@ -58,9 +66,8 @@
         adrne   lr, BSYM(1b)
         bne     do_local_timer
 #endif
-9997:
 #endif
-
+9997:
         .endm
 
 #ifdef CONFIG_KPROBES
@@ -1245,3 +1252,9 @@ cr_alignment:
         .space  4
 cr_no_alignment:
         .space  4
+
+#ifdef CONFIG_MULTI_IRQ_HANDLER
+        .globl  handle_arch_irq
+handle_arch_irq:
+        .space  4
+#endif