[PATCH] ARM: Allow machine to specify it's own IRQ handlers at run-time

[eric.y.miao@gmail.com (Eric Miao)]

On Sun, Dec 5, 2010 at 5:23 PM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Mon, Nov 22, 2010 at 04:26:50PM +0800, Eric Miao wrote:
>> I wonder if it's still acceptable for a patch like below to have a dynamic IRQ
>> handler at run-time. There is some changes to the irq_handler, esp. some
>> SMP changes.
>>
>> Magnus had some similar patches to have a run-time irq_handler, which is
>> a bit more complicated, but I'm also very happy with.
>
> I'd prefer a simple but efficient approach. ?I am worried about
> unnecessarily increasing the IRQ latency - and IRQ latency is something
> that we should be concerned about. ?It has the ability to make platforms
> useless.
>
> Eg, we know that SMC91x net interfaces are sensitive to IRQ latency, and
> the same is true of serial ports with small FIFOs.
>
> Any attempt to support multiple IRQ handlers is going to increase IRQ
> handling latency - I don't think that's something which can be avoided,
> and I'm wondering what effect this and the recent genirq changes is going
> to have. ?Has anyone been keeping an eye on IRQ handling latency?
>
> Lastly, this patch is dependent on your machine class patches, which makes
> it unsuitable as-is for mainline.
>

This one isn't. I've rebased this on top of v2.6.37-rc1.

>> commit d57e464929c9b2b50cda07e8683679583adf0fee
>> Author: Eric Miao <eric.y.miao@gmail.com>
>> Date: ? Mon Nov 22 16:13:51 2010 +0800
>>
>> ? ? ARM: 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 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.
>> ? ? And the IPI stuff on SMP is expected to move to the provided arch
>> ? ? IRQ handler as well.
>>
>> ? ? Signed-off-by: Eric Miao <eric.miao@canonical.com>
>> ? ? Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
>>
>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>> index a19a526..c2c9838 100644
>> --- a/arch/arm/Kconfig
>> +++ b/arch/arm/Kconfig
>> @@ -1017,6 +1017,11 @@ 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 d97a964..7d55356 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 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 c09e357..8ed4f7c 100644
>> --- a/arch/arm/kernel/entry-armv.S
>> +++ b/arch/arm/kernel/entry-armv.S
>> @@ -29,6 +29,7 @@
>> ?/*
>> ? * 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
>> @@ -62,6 +63,14 @@
>> ?#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
>> @@ -1245,3 +1254,9 @@ 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 336f14e..a834c6c 100644
>> --- a/arch/arm/kernel/setup.c
>> +++ b/arch/arm/kernel/setup.c
>> @@ -876,6 +876,12 @@ void __init setup_arch(char **cmdline_p)
>> ? ? ? system_timer = mdesc->timer;
>> ? ? ? init_machine = mdesc->init_machine;
>>
>> +#ifdef CONFIG_MULTI_IRQ_HANDLER
>> + ? ? handle_arch_irq = class ? class->handle_irq : NULL;
>> + ? ? if (!handle_arch_irq)
>> + ? ? ? ? ? ? panic("No machine class specific IRQ handler defined\n");
>> +#endif
>> +
>> ?#ifdef CONFIG_VT
>> ?#if defined(CONFIG_VGA_CONSOLE)
>> ? ? ? conswitchp = &vga_con;
>