On 17 April 2015 at 17:02, Tomeu Vizoso <tomeu.viz...@collabora.com> wrote: > On 17 April 2015 at 16:08, Lorenzo Pieralisi <lorenzo.pieral...@arm.com> > wrote: >> On Thu, Apr 16, 2015 at 03:37:19PM +0100, Tomeu Vizoso wrote: >> >> [...] >> >>> >> I don't know what FIQs are. :-) >>> > >>> > In short, fast IRQs, it is a separate IRQ line handled as a separate >>> > exception source with some private (banked) registers that minimize >>> > registers >>> > saving/restoring. They are not identical to NMI on x86, since >>> > their behaviour (handling) may be overriden by platforms and they >>> > can be masked. >>> > >>> >> ->enter_freeze is entered with interrupts disabled on the local CPU. It >>> >> is >>> >> not supposed to re-enable them. That is, while in the ->enter_freeze >>> >> callback >>> >> routine, the CPU must not be interrupted aby anything other than NMI. >>> > >>> > It boils down to what FIQs handlers are allowed to do with tick frozen >>> > and what they are (may be) currently used for. >>> > >>> > Russell has more insights on this than I do, in particular what FIQs are >>> > currently used for on ARM and if we can leave them enabled safely with >>> > tick >>> > frozen. >>> >>> But even if it's currently safe to leave them enabled, is there any >>> reason for not disabling them? >> >> Ok, the point here is: either it is safe, and you leave them enabled, >> or it is not and we must disable them *before* enter_freeze() is entered. >> >> Disabling them in the platform enter_freeze() hook does not make sense, >> because this means we run with FIQs enabled with tick frozen, either >> it is safe or it is not, it can't be both. > > Sure, that's why I proposed doing it in arch_cpu_idle_enter/exit. > >> I would ask Russell opinion on this, before making any decision. > > Sure, that would be very welcome.
Hi Russell, do you think FIQs should be disabled when the tick is frozen when going to suspend to idle? Thanks, Tomeu -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
