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>

5 files changed, 30 insertions, 2 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index fd0e21be5e44..47694865018c 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1022,6 +1022,11 @@ config CPU_HAS_PMU
         default y
         bool
 
+config MULTI_IRQ_HANDLER
+        bool
+        help
+          Allow each machine to specify it's own IRQ handler at run time.
+
 if !MMU
 source "arch/arm/Kconfig-nommu"
 endif
diff --git a/arch/arm/include/asm/mach/arch.h b/arch/arm/include/asm/mach/arch.h
index d97a964207fa..7d55356110d4 100644
--- a/arch/arm/include/asm/mach/arch.h
+++ b/arch/arm/include/asm/mach/arch.h
@@ -40,6 +40,9 @@ struct machine_desc {
         void                    (*init_irq)(void);
         struct sys_timer        *timer;         /* system tick timer    */
         void                    (*init_machine)(void);
+#ifdef CONFIG_MULTI_IRQ_HANDLER
+        void                    (*handle_irq)(struct pt_regs *);
+#endif
 };
 
 /*
diff --git a/arch/arm/include/asm/mach/irq.h b/arch/arm/include/asm/mach/irq.h
index ce3eee9fe26c..6ecdad9a5c42 100644
--- a/arch/arm/include/asm/mach/irq.h
+++ b/arch/arm/include/asm/mach/irq.h
@@ -22,6 +22,10 @@ extern void (*init_arch_irq)(void);
 extern void init_FIQ(void);
 extern int show_fiq_list(struct seq_file *, void *);
 
+#ifdef CONFIG_MULTI_IRQ_HANDLER
+extern void (*handle_arch_irq)(struct pt_regs *);
+#endif
+
 /*
  * This is for easy migration, but should be changed in the source
  */
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
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 8075e592f902..0826f36330c4 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -875,6 +875,9 @@ void __init setup_arch(char **cmdline_p)
         init_arch_irq = mdesc->init_irq;
         system_timer = mdesc->timer;
         init_machine = mdesc->init_machine;
+#ifdef CONFIG_MULTI_IRQ_HANDLER
+        handle_arch_irq = mdesc->handle_irq;
+#endif
 
 #ifdef CONFIG_VT
 #if defined(CONFIG_VGA_CONSOLE)