On Fri, Mar 6, 2015 at 12:06 PM, Mark Rutland <mark.rutland@xxxxxxx> wrote: > [...] > >> > The request_irq path never results in a call to chip->irq_set_wake(), >> > even with the IRQF_NO_SUSPEND flag. So requesting an irq with >> > IRQF_NO_SUSPEND does not guarantee wakeup; it only guarantees that the >> > CPU can take the interrupt _around_ the suspended state, not necessarily >> > while _in_ the suspended state. >> >> Right. "Suspended state" meaning full suspend here I suppose? > > Yes; any state deeper than suspend-to-idle. > > [...] > >> > We seem to be conflating some related properties: >> > >> > [a] The IRQ will be left unmasked. >> > [b] The IRQ will be handled immediately when taken. >> > [c] The IRQ will wake the system from suspend. >> > >> > Requesting an IRQ with IRQF_NO_SUSPEND guarantees [a,b], but does not >> > guarantee [c]. >> >> That's correct. IRQF_NO_SUSPEND does not guarantee that interrupts from >> that IRQ will have any effect after arch_suspend_disable_irqs() in >> suspend_enter(). > > [...] > >> > It sounds like for this kind of watchdog device we want [a,b,c], even if >> > the IRQ is not shared with an IRQF_NO_SUSPEND user. >> >> We can't guarantee that, though. arch_suspend_disable_irqs() disables >> interrupts on the last working CPU and it won't get any. It may be >> brought out of a low-power state by a pending interrupt, but it won't act >> upon that interrupt immediately anyway, only after the arch_suspend_enable_irqs() >> in suspend_enter(). > > Ok, so [b] needs the caveat that it's only handled "immediately" outside > of the arch_suspend_disable_irqs() ... arch_suspend_enable_irqs() > section. > >> But then it might as well be deferred until after >> resume_device_irqs(). > > That was my original line of thinking, in which case the watchdog driver > should use IRQF_COND_SUSPEND rather than IRQF_NO_SUSPEND, with > enable_irq_wake() if we care about the watchdog during suspend. I'm > happy with this. > > Considering that the use-case of a watchdog is to alert us to something > going hideously wrong in the kernel, we want to handle the IRQ after > executing the smallest amount of kernel code possible. For that, they > need to have their handlers to be called "immediately" outside of the > arch_suspend_disable_irqs() ... arch_suspend_enable_irqs() window, and > need to be enabled during suspend to attempt to catch bad wakeup device > configuration. > > I think it's possible (assuming the caveats on [b] above) to provide > [a,b,c] for this case. OK But in this case the request_irq() passing IRQF_NO_SUSPEND *and* requiring enable_irq_wake() in addition to that needs a big fat comment explaining the whole thing or we'll forget about the gory details at one point and no one will know what's going on in there. Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
