Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964802AbVI0EmM (ORCPT ); Tue, 27 Sep 2005 00:42:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964803AbVI0EmM (ORCPT ); Tue, 27 Sep 2005 00:42:12 -0400 Received: from colo.lackof.org ([198.49.126.79]:25805 "EHLO colo.lackof.org") by vger.kernel.org with ESMTP id S964802AbVI0EmL (ORCPT ); Tue, 27 Sep 2005 00:42:11 -0400 Date: Mon, 26 Sep 2005 22:48:40 -0600 From: Grant Grundler To: "Randy.Dunlap" Cc: lkml , akpm , gregkh , linux-pci@atrey.karlin.mff.cuni.cz, ak@suse.de Subject: Re: [PATCH] MSI interrupts: disallow when no LAPIC/IOAPIC support Message-ID: <20050927044840.GA21108@colo.lackof.org> References: <20050926201156.7b9ef031.rdunlap@xenotime.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050926201156.7b9ef031.rdunlap@xenotime.net> X-Home-Page: http://www.parisc-linux.org/ User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1457 Lines: 41 On Mon, Sep 26, 2005 at 08:11:56PM -0700, Randy.Dunlap wrote: > From: Randy Dunlap > > MSI requires local APIC + IO APIC support (according to > drivers/pci/Kconfig), The purpose of MSI is to bypass the IO APIC. I'm not aware of any dependency on IO APIC in HW. I suspect the dependency in the Kconfig is historical because of how the x86 source code is structured: config X86_LOCAL_APIC bool depends on X86_UP_APIC || ((X86_VISWS || SMP) && !X86_VOYAGER) default y essentially, LOCAL_APIC gets enabled if "UP_APIC or SMP". I've no clue why folks thought it was better to ignore the IO APIC on UP kernels. I'm pretty sure one only needs a local APIC support. Local APIC responds to 0xfee00000 range of addresses and directs the interrupt to a CPU. > but if a kernel is built with all of > those (APICs + CONFIG_PCI_MSI) and then booted with "nosmp" or > "max_cpus=0|1" or "noapic" or "nolapic", MSI also should be > disabled, otherwise the interrupt routing is bad (so that only > using "irqpoll" helps). UP vs SMP is orthogonal to MSI support wrt HW. I suppose this is another historical artifact of APICs being used with SMP x86 boxes first. thanks, grant - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/