On 11/04/16 16:31, Jon Hunter wrote: > Hi Mark, > > On 09/04/16 11:58, Marc Zyngier wrote: >> On Thu, 17 Mar 2016 15:04:01 +0000 >> Jon Hunter <jonathanh@xxxxxxxxxx> 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? It depends where you plan to handle the error. Ideally, I'd keep on returning the error (because that's the right thing to do), and move the WARN_ON() into the core code. We'd keep on ignoring the error as we're doing today, but we'd scream about it. After a couple of releases, we'd turn the WARN_ON into a hard fail. Thoughts? 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@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
