Subject: Re: [PATCH 1/2] mpparse: Add a knob to disable IRQ 0 through I/O APIC

From: Randy Dunlap <[email-masked]>
Date: Mon, 30 Jun 2008 21:57:46 -0700

On Tue, 1 Jul 2008 01:11:35 +0100 (BST) Maciej W. Rozycki wrote:

>  As discovered recently some systems exhibit problems when the 8254 timer 
> IRQ is routed through the I/O APIC.  These problems do not affect the 
> timer IRQ itself and therefore cannot be detected when the correctness of 
> operation of the interrupt is verified in check_timer().  Therefore the 
> I/O APIC path of the timer IRQ has to be disabled entirely.
> 
>  This is a change that lets platforms ask for the timer IRQ not to be 
> registered in the I/O APIC interrupt tables.  The local APIC and ExtINTA 
> paths are unaffected.  This request is only taken into account for ACPI 
> platforms as MP table systems seem unaffected so far.
> 
> Signed-off-by: Maciej W. Rozycki <[email-masked]>
> ---
> patch-2.6.26-rc1-20080505-mpparse-acpi-noirq0-2
> diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/arch/x86/kernel/mpparse.c linux-2.6.26-rc1-20080505/arch/x86/kernel/mpparse.c
> --- linux-2.6.26-rc1-20080505.macro/arch/x86/kernel/mpparse.c	2008-05-05 02:56:19.000000000 +0000
> +++ linux-2.6.26-rc1-20080505/arch/x86/kernel/mpparse.c	2008-06-30 21:53:33.000000000 +0000
> @@ -50,6 +50,8 @@ static int mp_current_pci_id;
>  
>  int pic_mode;
>  
> +int disable_irq0_through_ioapic __initdata;
> +
>  /*
>   * Intel MP BIOS table parsing routines:
>   */
> @@ -887,6 +889,10 @@ void __init mp_override_legacy_irq(u8 bu
>  	int ioapic = -1;
>  	int pin = -1;
>  
> +	/* Skip the 8254 timer interrupt (IRQ 0) if requested.  */
> +	if (bus_irq == 0 && disable_irq0_through_ioapic)
> +		return;
> +
>  	/*
>  	 * Convert 'gsi' to 'ioapic.pin'.
>  	 */
> @@ -955,6 +961,10 @@ void __init mp_config_acpi_legacy_irqs(v
>  	for (i = 0; i < 16; i++) {
>  		int idx;
>  
> +		/* Skip the 8254 timer interrupt (IRQ 0) if requested.  */
> +		if (i == 0 && disable_irq0_through_ioapic)
> +			continue;
> +
>  		for (idx = 0; idx < mp_irq_entries; idx++) {
>  			struct mpc_config_intsrc *irq = mp_irqs + idx;
>  
> diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/include/asm-x86/mpspec.h linux-2.6.26-rc1-20080505/include/asm-x86/mpspec.h
> --- linux-2.6.26-rc1-20080505.macro/include/asm-x86/mpspec.h	2008-05-05 02:55:57.000000000 +0000
> +++ linux-2.6.26-rc1-20080505/include/asm-x86/mpspec.h	2008-06-30 22:29:23.000000000 +0000
> @@ -113,4 +113,15 @@ typedef struct physid_mask physid_mask_t
>  
>  extern physid_mask_t phys_cpu_present_map;
>  
> +#ifdef CONFIG_X86_MPPARSE
> +static inline void set_disable_irq0_through_ioapic(int v)
> +{
> +	extern int disable_irq0_through_ioapic;
> +
> +	disable_irq0_through_ioapic = v;
> +}
> +#else
> +static inline void set_disable_irq0_through_ioapic(int v) { }
> +#endif
> +
>  #endif

What calls set_disable_irq0_through_ioapic() ?

---
~Randy
Linux Plumbers Conference, 17-19 September 2008, Portland, Oregon USA
http://linuxplumbersconf.org/