linux-kernel - Re: [patch 26/26] x64, x2apic/intr-remap: introduce CONFIG_INTR

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Date:	Thu, 10 Jul 2008 16:29:59 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	mingo@...e.hu, hpa@...or.com, tglx@...utronix.de,
	akpm@...ux-foundation.org, arjan@...ux.intel.com,
	andi@...stfloor.org, ebiederm@...ssion.com,
	jbarnes@...tuousgeek.org, steiner@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 26/26] x64, x2apic/intr-remap: introduce CONFIG_INTR_REMAP

Suresh Siddha <suresh.b.siddha@...el.com> writes:

> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> ---
>
> Index: tree-x86/arch/x86/Kconfig
> ===================================================================
> --- tree-x86.orig/arch/x86/Kconfig	2008-07-10 09:51:44.000000000 -0700
> +++ tree-x86/arch/x86/Kconfig	2008-07-10 09:52:43.000000000 -0700
> @@ -1657,6 +1657,14 @@
>  	 workaround will setup a 1:1 mapping for the first
>  	 16M to make floppy (an ISA device) work.
>  
> +config INTR_REMAP
> +	bool "Support for Interrupt Remapping (EXPERIMENTAL)"
> +	depends on X86_64 && X86_IO_APIC && PCI_MSI && ACPI && EXPERIMENTAL
> +	help
> +	 Supports Interrupt remapping for IO-APIC and MSI devices.
> +	 To use x2apic mode in the CPU's which support x2APIC enhancements or
> +	 to support platforms with CPU's having > 8 bit APIC ID, say Y.
> +

This has got to be the strangest config option.
X86_IO_APIC makes sense.  Fundamentally it is the wrong config option but that
isn't the fault of your code.

PCI_MSI should not matter.

Is it possible to run in x2apic mode without running in interrupt remapping mode?
Just send the irqs directly to the cpu?  It feels like it should be if an iommu
doesn't get in the way.

Eric
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