From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [Patch V4 12/42] x86, ioapic: kill static variable nr_irqs_gsi Date: Thu, 12 Jun 2014 12:58:37 +0200 (CEST) Message-ID: References: <1402302011-23642-1-git-send-email-jiang.liu@linux.intel.com> <1402302011-23642-13-git-send-email-jiang.liu@linux.intel.com> <53969834.3040404@linux.intel.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Return-path: Received: from www.linutronix.de ([62.245.132.108]:39500 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751788AbaFLK7K (ORCPT ); Thu, 12 Jun 2014 06:59:10 -0400 In-Reply-To: <53969834.3040404@linux.intel.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Jiang Liu Cc: Benjamin Herrenschmidt , Grant Likely , Ingo Molnar , "H. Peter Anvin" , "Rafael J. Wysocki" , Bjorn Helgaas , Randy Dunlap , Yinghai Lu , x86@kernel.org, Konrad Rzeszutek Wilk , Andrew Morton , Tony Luck , Joerg Roedel , Paul Gortmaker , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-acpi@vger.kernel.org, Ingo Molnar On Tue, 10 Jun 2014, Jiang Liu wrote: > Hi Thomas, > This piece of code is inherited from current IOAPIC driver > and I think it's a workaround for some weird platforms. > For normal platforms with both 8259A and IOAPIC controllers, > legacy ISA IRQs should be connected to both 8259A and IOAPIC pins > (ignore timer and cascade IRQs for simplicity). According to comments > in current kernel, there are some platforms on which: > 1) some ISA IRQs are only connected to 8259A controllers. > 2) the corresponding IOAPIC pins are connected to some non-ISA IRQs. > For such platforms, IRQ0-15 are used for ISA IRQs and another > 16 IRQs just above gsi_top are reserved for IOAPIC pins 0-15 which > are connected to non-ISA IRQs. > I have no real experience with such a platform, but just > guessing possible cases according to kernel comments and "Multiple > Processor Specification". Please look at these two pictures for quick > reference. > http://www.manualslib.com/manual/77733/Intel-Multiprocessor.html?page=31#manual > http://www.manualslib.com/manual/77733/Intel-Multiprocessor.html?page=63#manual Duh. I completely forgot about the 82489 mess. We probably want a comment somewhere why we have this gsi + legacy thing. Thanks, tglx