[RFC PATCH 1/2] allow each machine to specify it's own IRQ handlers at run-time

[Eric Miao]

commit edec494b3dbf52a61a18b484dd05cce6a9d90e2f
Author: Eric Miao <eric.y.miao at gmail.com>
Date:   Sat May 22 11:58:01 2010 +0800

    [ARM] allow each 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 class 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.

    Signed-off-by: Eric Miao <eric.y.miao at gmail.com>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ddf5676..a8f5f78 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -958,6 +958,11 @@ 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 5ee6f85..b611895 100644
--- a/arch/arm/include/asm/mach/arch.h
+++ b/arch/arm/include/asm/mach/arch.h
@@ -42,6 +42,9 @@ 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 ce3eee9..6ecdad9 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 7ee48e7..ecb8492 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -28,6 +28,7 @@
 /*
  * Interrupt handling.  Preserves r7, r8, r9
  */
+#ifndef CONFIG_MULTI_IRQ_HANDLER
 	.macro	irq_handler
 	get_irqnr_preamble r5, lr
 1:	get_irqnr_and_base r0, r6, r5, lr
@@ -59,6 +60,14 @@
 #endif

 	.endm
+#else
+	.macro	irq_handler
+	ldr	r4, =handle_arch_irq
+	mov	r0, sp
+	mov	lr, pc
+	ldr	pc, [r4]
+	.endm
+#endif	/* CONFIG_MULTI_IRQ_HANDLER */

 #ifdef CONFIG_KPROBES
 	.section	.kprobes.text,"ax",%progbits
@@ -1251,3 +1260,9 @@ cr_alignment:
 	.space	4
 cr_no_alignment:
 	.space	4
+
+#ifdef CONFIG_MULTI_IRQ_HANDLER
+	.globl	handle_arch_irq
+handle_arch_irq:
+	.long	0
+#endif
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index f1aee0d..61d5f8d 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -732,6 +732,10 @@ void __init setup_arch(char **cmdline_p)
 	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)
 	conswitchp = &vga_con;