Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754697AbcDKPbg (ORCPT ); Mon, 11 Apr 2016 11:31:36 -0400 Received: from hqemgate16.nvidia.com ([216.228.121.65]:2360 "EHLO hqemgate16.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750879AbcDKPbd (ORCPT ); Mon, 11 Apr 2016 11:31:33 -0400 X-PGP-Universal: processed; by hqnvupgp08.nvidia.com on Mon, 11 Apr 2016 08:29:49 -0700 Subject: Re: [PATCH 04/15] irqchip/gic: WARN if setting the interrupt type fails To: Marc Zyngier References: <1458224359-32665-1-git-send-email-jonathanh@nvidia.com> <1458224359-32665-5-git-send-email-jonathanh@nvidia.com> <56EAC761.1040801@nvidia.com> <20160409115854.492090a5@arm.com> CC: Thomas Gleixner , Jason Cooper , =?UTF-8?Q?Beno=c3=aet_Cousson?= , Tony Lindgren , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Stephen Warren , Thierry Reding , Kevin Hilman , Geert Uytterhoeven , Grygorii Strashko , Lars-Peter Clausen , Linus Walleij , , , , From: Jon Hunter Message-ID: <570BC34A.5030806@nvidia.com> Date: Mon, 11 Apr 2016 16:31:22 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <20160409115854.492090a5@arm.com> X-Originating-IP: [10.21.132.108] X-ClientProxiedBy: UKMAIL101.nvidia.com (10.26.138.13) To UKMAIL101.nvidia.com (10.26.138.13) Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3451 Lines: 73 Hi Mark, On 09/04/16 11:58, Marc Zyngier wrote: > On Thu, 17 Mar 2016 15:04:01 +0000 > Jon Hunter wrote: > >> >> On 17/03/16 14:51, Thomas Gleixner wrote: >>> On Thu, 17 Mar 2016, Jon Hunter wrote: >>> >>>> Setting the interrupt type for private peripheral interrupts (PPIs) may >>>> not be supported by a given GIC because it is IMPLEMENTATION DEFINED >>>> whether this is allowed. There is no way to know if setting the type is >>>> supported for a given GIC and so the value written is read back to >>>> verify it matches the desired configuration. If it does not match then >>>> an error is return. >>>> >>>> There are cases where the interrupt configuration read from firmware >>>> (such as a device-tree blob), has been incorrect and hence >>>> gic_configure_irq() has returned an error. This error has gone >>>> undetected because the error code returned was ignored but the interrupt >>>> still worked fine because the configuration for the interrupt could not >>>> be overwritten. >>>> >>>> Given that this has done undetected and we should only fail to set the >>>> type for PPIs whose configuration cannot be changed anyway, don't return >>>> an error and simply WARN if this fails. This will allows us to fix up any >>>> places in the kernel where we should be checking the return status and >>>> maintain back compatibility with firmware images that may have incorrect >>>> interrupt configurations. >>> >>> Though silently returning 0 is really the wrong thing to do. You can add the >>> warn, but why do you want to return success? >> >> Yes that would be the correct thing to do I agree. However, the problem >> is that if we do this, then after the patch "irqdomain: Don't set type >> when mapping an IRQ" is applied, we may break interrupts for some >> existing device-tree binaries that have bad configuration (such as omap4 >> and tegra20/30 ... see patches 1 and 2) that have gone unnoticed. So it >> is a back compatibility issue. >> >> If you are wondering why these interrupts break after "irqdomain: Don't >> set type when mapping an IRQ", it is because today >> irq_create_fwspec_mapping() does not check the return code from setting >> the type, but if we defer setting the type until __setup_irq() which >> does check the return code, then all of a sudden interrupts that were >> working (even with bad configurations) start to fail. >> >> The reason why I opted not to return an error code from >> gic_configure_irq() is it really can't fail. The failure being reported >> does not prevent the interrupt from working, but tells you your >> configuration does not match the hardware setting which you cannot >> overwrite. >> >> So to maintain back compatibility and avoid any silent errors, I opted >> to make it a WARN and not return an error. >> >> If people are ok with potentially breaking interrupts for device-tree >> binaries with bad settings, then I am ok to return an error here. > > I think we need to phase things. Let's start with warning people for a > few kernel releases. Actively maintained platforms will quickly address > the issue (fixing their DT). As I see it, this issue seems rather > widespread (even kvmtool outputs a DT with the wrong triggering > information). > > Once we've fixed the bulk of the platforms and virtual environments, we > can start thinking about making it fail harder. Ok, so are you OK with this patch as-is? If so, can I add your ACK? Cheers Jon