On Fri, Mar 06, 2015 at 11:06:18AM +0000, Mark Rutland 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. I don't think we should want to make such distinction; we should treat all suspend states the same. Drivers should not want to rely on the fact that one state (suspend-to-idle) might maybe deal with interrupts while other states do not. > > > 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. Note that COND_SUSPEND must have SHARED set. > 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. While I appreciate the use-case; we should be careful not to make of mess of things either. -- 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
