On Mon, Dec 01, 2014 at 11:32:00AM +0100, Tim Sander wrote: > Hi Russel, Daniel > > Am Freitag, 28. November 2014, 10:08:28 schrieb Russell King - ARM Linux: > > The two things are mutually exclusive. You can either have FIQ being used > > for debug purposes, where we decode the FIQ reason and call some function > > (which means that we will only service one FIQ at a time) or you can use > > it in exclusive mode (provided by fiq.c) where your handler has sole usage > > of the vector, and benefits from fast and immediate servicing of the event. > > As far as i am aware, die CONFIG_FIQ symbol is not pulled by all ARM > platforms. Since there are ARM platforms which don't use this symbol but the > hardware is fully capable of handling FIQ requests i would expect, that adding > CONFIG_FIQ to a plattform, that this platform honors the set_fiq_handler > functionality.
That whole paragraph doesn't make much sense to me. Look, in my mind it is very simple. If you are using CONFIG_FIQ on a SMP platform, your life will be very difficult. The FIQ code enabled by that symbol is not designed to be used on SMP systems, *period*. If you decide to enable CONFIG_FIQ, and you use that code on a SMP platform, I'm going to say right now so it's totally clear: if you encounter a problem, I don't want to know about it. The code is not designed for use on that situation. Therefore, as far as I'm concerned, the two facilities are mututally exclusive. I had thought about whether the IPI FIQ should be disabled when a replacement FIQ handler is installed, I deem it not to be a use case that the mainline kernel needs to be concerned about. > Yes, but if the FIQ handler is also used for IPI, set_fiq_handler gets IPI > interrupts (with the patch starting this thread)? So i think that the patch > needs to look like: > --- a/arch/arm/kernel/traps.c > +++ b/arch/arm/kernel/traps.c > @@ -483,6 +483,9 @@ asmlinkage void __exception_irq_entry > handle_fiq_as_nmi(struct pt_regs *regs) > +#ifndef CONFIG_FIQ > #ifdef CONFIG_ARM_GIC > gic_handle_fiq_ipi(); > #endif > +#endif No. With a single zImage kernel, you could very well have SMP and FIQ both enabled, but have a non-SMP platform using FIQ, but also support SMP platforms as well. Your change prevents that happening. -- FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
