Re: [PATCH] x86: APIC: Remove apic_write_around(); use alternatives

[Yong Wang <yong.y.wang@linux.intel.com>]

On Mon, Jul 21, 2008 at 10:59:41AM -0700, Suresh Siddha wrote:
> Thanks Ingo. I tested tip/master and found an issue (patch attached)
> for x2apic support. This is not because of the recent merges we had, but
> because of something(where we still access memory based interface after
> enabling x2apic mode) that slipped through my earlier tests.
> 
> Probably it is a good idea to unmap the memory mapped interface, once we switch
> to x2apic mode. That will catch the issues much earlier. I will
> post another patch for this.
> 
> Meanwhile, I will do more testing of tip/master along with addressing
> open issues.
> ---
> 
> [patch] x64, apic: use generic apic_write() for ack_APIC_irq()
> 
> ack_APIC_irq() is used at too many generic places (and not just during
> irq_chip handling!) to use the native_apic_mem_write(). For ex, this will
> break x2apic based systems.
> 
> Fix ack_APIC_irq() to use the generic apic_write() even for 64-bit.
> 
> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
> ---
> 
> diff --git a/include/asm-x86/apic.h b/include/asm-x86/apic.h
> index 300b65e..1df955f 100644
> --- a/include/asm-x86/apic.h
> +++ b/include/asm-x86/apic.h
> @@ -138,11 +138,7 @@ static inline void ack_APIC_irq(void)
>  	 */
>  
>  	/* Docs say use 0 for future compatibility */
> -#ifdef CONFIG_X86_32
>  	apic_write(APIC_EOI, 0);
> -#else
> -	native_apic_mem_write(APIC_EOI, 0);
> -#endif
>  }
>  

ACK. I tested this patch on my x2apic capable box and it works well. Without this patch, kernel built from tip/x86/x2apic cannot boot in x2apic mode and all APs got stuck in smp_callin->calibrate_delay and failed to boot. After applying this patch, system boots well and all processors got up and running successfully.