Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752343Ab3HOWSu (ORCPT ); Thu, 15 Aug 2013 18:18:50 -0400 Received: from mail.active-venture.com ([67.228.131.205]:55936 "EHLO mail.active-venture.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751481Ab3HOWSt (ORCPT ); Thu, 15 Aug 2013 18:18:49 -0400 X-Originating-IP: 108.223.40.66 Message-ID: <520D53CA.6040807@roeck-us.net> Date: Thu, 15 Aug 2013 15:18:50 -0700 From: Guenter Roeck User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130803 Thunderbird/17.0.8 MIME-Version: 1.0 To: Peter Maydell CC: Russell King - ARM Linux , Paul Gortmaker , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , QEMU Developers , Arnd Bergmann Subject: Re: [Qemu-devel] SCSI bus failures with qemu-arm in kernel 3.8+ References: <5207B3C3.9080508@roeck-us.net> <20130811220450.GY23006@n2100.arm.linux.org.uk> <52082EF8.10005@roeck-us.net> <20130813034054.GA18218@roeck-us.net> <20130815175428.GA18580@roeck-us.net> <20130815205044.GA21599@roeck-us.net> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1912 Lines: 40 On 08/15/2013 02:49 PM, Peter Maydell wrote: > On 15 August 2013 21:50, Guenter Roeck wrote: >> On Thu, Aug 15, 2013 at 07:05:22PM +0100, Peter Maydell wrote: >>> It needs to go in the same patch, because a kernel with the fixed >>> irq remapping must also tell QEMU it is fixed; if you split the >>> two then at the point between the two patches the kernel is >>> broken for bisection purposes. >>> >> Thinking about it - is that really true ? My image with the >> patch applied works just fine under qemu 1.5.2, and unless >> I am missing something it won't work with qemu 1.4 anyway. >> So what exactly is broken ? > > You're OK unless the kernel happens to pick the same interrupt > number to write to PCI_INTERRUPT_LINE as one of the previous > broken kernel versions did (in which case QEMU will incorrectly > assume you're a broken kernel). This can't happen with the way > the kernel is currently picking interrupt numbers (ie with a > straightforward relationship between h/w irqs and values written), > but as I understand from Arnd there is a plan to move to a > different approach ("sparse irqs") at which point this won't hold: > http://lists.gnu.org/archive/html/qemu-devel/2013-03/msg04579.html > So it's better for the kernel to make sure it gets the > behaviour it wants rather than getting unpleasant surprises > later. > But doesn't that mean that there is _currently_ no problem ? If so, we can introduce the additional code when the problem really shows up. Being Preemptive is good, but if it is not really needed today I would rather have today's problems resolved and bother about tomorrow's when they show up. Guenter -- 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/