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? Cheers Jon -- 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
