From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758524AbXKGN1n (ORCPT ); Wed, 7 Nov 2007 08:27:43 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756780AbXKGN11 (ORCPT ); Wed, 7 Nov 2007 08:27:27 -0500 Received: from pip10.gyao.ne.jp ([61.122.117.248]:59137 "EHLO mx.gate01.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755892AbXKGN1Z (ORCPT ); Wed, 7 Nov 2007 08:27:25 -0500 Date: Wed, 7 Nov 2007 22:27:02 +0900 From: Paul Mundt To: Alan Cox 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: <20071107132702.GA27488@linux-sh.org> Mail-Followup-To: Paul Mundt , Alan Cox , Jeff Garzik , Andrew Morton , linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org, linuxsh-dev@lists.sourceforge.net References: <20071107081052.GA25913@linux-sh.org> <20071107130940.16b5ea86@the-village.bc.nu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071107130940.16b5ea86@the-village.bc.nu> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 07, 2007 at 01:09:40PM +0000, Alan Cox wrote: > On Wed, 7 Nov 2007 17:10:52 +0900 > Paul Mundt wrote: > > By default ata_host_activate() expects a valid IRQ in order to > > successfully register the host. This patch enables a special case > > for registering polling-only hosts that either don't have IRQs > > or have buggy IRQ generation (either in terms of handling or > > sensing), which otherwise work fine. > > > > Hosts that want to use polling mode can simply set ATA_FLAG_PIO_POLLING > > and pass in a NULL IRQ handler or invalid (< 0) IRQ. > > NAK > > 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. 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.