Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964822AbWEBNxO (ORCPT ); Tue, 2 May 2006 09:53:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964825AbWEBNxO (ORCPT ); Tue, 2 May 2006 09:53:14 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:8655 "EHLO ebiederm.dsl.xmission.com") by vger.kernel.org with ESMTP id S964822AbWEBNxM (ORCPT ); Tue, 2 May 2006 09:53:12 -0400 To: Andi Kleen Cc: "Brown, Len" , "Protasevich, Natalie" , sergio@sergiomb.no-ip.org, "Kimball Murray" , linux-kernel@vger.kernel.org, akpm@digeo.com, kmurray@redhat.com, linux-acpi@vger.kernel.org Subject: [RFC][PATCH] Document what in IRQ is. References: <200605020946.46050.ak@suse.de> From: ebiederm@xmission.com (Eric W. Biederman) Date: Tue, 02 May 2006 07:52:22 -0600 In-Reply-To: <200605020946.46050.ak@suse.de> (Andi Kleen's message of "Tue, 2 May 2006 09:46:45 +0200") Message-ID: User-Agent: Gnus/5.1007 (Gnus v5.10.7) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1790 Lines: 47 Andi Kleen writes: > P.S.: There seems to be a lot of confusion about all this. > Maybe it would make sense to do a write up defining all the terms > and stick it into Documentation/* ? How does this look? I am pretty horrible when it comes to Documentation, but this seems to be the essence of what I was saying earlier. Eric diff --git a/Documentation/IRQ.txt b/Documentation/IRQ.txt new file mode 100644 index 0000000..5340369 --- /dev/null +++ b/Documentation/IRQ.txt @@ -0,0 +1,22 @@ +What is an IRQ? + +An IRQ is an interrupt request from a device. +Currently they can come in over a pin, or over a packet. +IRQs at the source can be shared. + +An IRQ number is a kernel identifier used to talk about a hardware +interrupt source. Typically this is an index into the global irq_desc +array, but except for what linux/interrupt.h implements the details +are architecture specific. + +An IRQ number is an enumeration of the possible interrupt sources on a +machine. Typically what is enumerated is the number of input pins on +all of the interrupt controller in the system. In the case of ISA +what is enumerated are the 16 input pins to the pair of i8259 +interrupt controllers. + +Architectures can assign additional meaning to the IRQ numbers, and +are encouraged to in the case where there is any manual configuration +of the hardware involved. The ISA IRQ case on x86 where anyone who +has been around a while can tell you how the first 16 IRQs map to the +input pins on a pair of i8259s is the classic example. - 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/