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. Thanks, M. -- Jazz is not dead. It just smells funny. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
