From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Zyngier Subject: Re: [PATCH 04/15] irqchip/gic: WARN if setting the interrupt type fails Date: Sat, 9 Apr 2016 11:58:54 +0100 Message-ID: <20160409115854.492090a5@arm.com> References: <1458224359-32665-1-git-send-email-jonathanh@nvidia.com> <1458224359-32665-5-git-send-email-jonathanh@nvidia.com> <56EAC761.1040801@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <56EAC761.1040801-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jon Hunter Cc: Thomas Gleixner , Jason Cooper , =?ISO-8859-1?Q?Beno=EEt?= 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 , linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-tegra@vger.kernel.org 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. Thanks, M. -- Jazz is not dead. It just smells funny. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752576AbcDIK7I (ORCPT ); Sat, 9 Apr 2016 06:59:08 -0400 Received: from foss.arm.com ([217.140.101.70]:42856 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752090AbcDIK7E (ORCPT ); Sat, 9 Apr 2016 06:59:04 -0400 Date: Sat, 9 Apr 2016 11:58:54 +0100 From: Marc Zyngier To: Jon Hunter Cc: Thomas Gleixner , Jason Cooper , =?ISO-8859-1?Q?Beno=EEt?= 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 , , , , Subject: Re: [PATCH 04/15] irqchip/gic: WARN if setting the interrupt type fails Message-ID: <20160409115854.492090a5@arm.com> In-Reply-To: <56EAC761.1040801@nvidia.com> References: <1458224359-32665-1-git-send-email-jonathanh@nvidia.com> <1458224359-32665-5-git-send-email-jonathanh@nvidia.com> <56EAC761.1040801@nvidia.com> Organization: ARM Ltd X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; arm-unknown-linux-gnueabihf) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanks, M. -- Jazz is not dead. It just smells funny.