From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755904AbXKGPSm (ORCPT ); Wed, 7 Nov 2007 10:18:42 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752973AbXKGPSe (ORCPT ); Wed, 7 Nov 2007 10:18:34 -0500 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:48536 "EHLO the-village.bc.nu" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1750758AbXKGPSd (ORCPT ); Wed, 7 Nov 2007 10:18:33 -0500 Date: Wed, 7 Nov 2007 15:18:37 +0000 From: Alan Cox To: Paul Mundt Cc: Jeff Garzik , Andrew Morton , linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org, linuxsh-dev@lists.sourceforge.net Subject: Re: [PATCH 1/2] libata: Support PIO polling-only hosts. Message-ID: <20071107151837.3cbe3a67@the-village.bc.nu> In-Reply-To: <20071107132702.GA27488@linux-sh.org> References: <20071107081052.GA25913@linux-sh.org> <20071107130940.16b5ea86@the-village.bc.nu> <20071107132702.GA27488@linux-sh.org> X-Mailer: Claws Mail 2.10.0 (GTK+ 2.10.14; i386-redhat-linux-gnu) Organization: Red Hat UK Cyf., Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SL4 1TE, Y Deyrnas Gyfunol. Cofrestrwyd yng Nghymru a Lloegr o'r rhif cofrestru 3798903 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > > Zero is "no IRQ", please use that for polling not "< 0" > > > However, platform_get_irq() will happily return IRQ#0, and it's a valid > vector on plenty of machines. NO_IRQ is also < 0 on at least FR-V, ARM, > blackin, PA-RISC, some PowerPC, and even IDE. No it is not. The platform IRQ code is responsible for ensuring that 0 is not a real IRQ and doing any neccessary remapping. Large parts of the kernel assume that - IRQ 0 is "no IRQ assigned" (serial, pci, ide etc ) - IRQ is *unsigned* > We do have some devices that are physically on IRQ#0 that otherwise work > fine, they aren't ATA devices mind you, but to claim that IRQ#0 isn't a > valid vector is not in line with what hardware actually does, whether > it's a good idea or not. In our case the IRQ vector maps to an exception > offset, which we bump down to zero. We could force an off-by-1 there so > that the math that indexes IRQ#0 is bumped up one, but that entails > fixing up every one of our IRQ numbers for no obvious gain. > > I don't really see any value in purposely crippling the range of > allowable vectors for these machines. Though I don't mind switching to a > NO_IRQ comparison instead of the < 0 case, so both can be handled. NO_IRQ is an obsolete old-IDE hack. http://www.uwsg.indiana.edu/hypermail/linux/kernel/0511.2/2197.html http://www.uwsg.indiana.edu/hypermail/linux/kernel/0511.2/1789.html Alan