Re: [PATCH] PM / wakeirq: report wakeup events in dedicated wake-IRQs

[Brian Norris <briannorris@chromium.org>]

On Fri, Nov 11, 2016 at 08:47:54AM -0800, Tony Lindgren wrote:
> But sounds like the threaded IRQ is not your concern and you mostly

Right, threaded is OK for this; it's not performance critical. It just
highlighted the fact that its completion is not synchronized with
anything.

> care about getting the right time for the wake up interrupt.

Not "time", per se, but blame. But that blame is timing related: if it
comes after the system finished resuming, then it's useless, since
user-space won't know to come back and check later.

> The wakeup interrupt controller knows something happened earlier,
> so maybe it could report that time if queried somehow?

Sort of. We have /sys/power/pm_wakeup_irq already. But it's really less
useful to get IRQ-level stats for this, than to get device info. AFAICT,
there's no machine-readable association between IRQs and devices; the
best you can get is by parsing the names in /proc/interrupts.

Or, if we really want to say that's sufficient, then maybe we should
kill all the device-level wakeup stats in sysfs... (Is that what the
flamewar was all about? I hope I'm not poking the hornet's nest.)

BTW, for context, I'm working on using dev_pm_set_dedicated_wake_irq()
for a Wifi driver which supports out-of-band (e.g., GPIO-based) wakeup.
I see it's used in the I2C core, but the I2C code never actually calls
dev_pm_enable_wake_irq(). So while I think I can use this API OK for
my Wifi driver (calling dev_pm_{en,dis}able_wake_irq() at system
suspend/resume), I'm not sure this will help the I2C case.

The more I look at this API, the more I'm confused, especially about its
seeming dependence on runtime PM.

Brian