Re: [PATCH] rtc: imxdi: add wakeup support

[Alexandre Belloni]

On 04/05/2021 12:08:58+0200, Martin Kaiser wrote:
> Thus wrote Alexandre Belloni (alexandre.belloni@xxxxxxxxxxx):
> 
> > >  	platform_set_drvdata(pdev, imxdi);
> 
> > > +	device_set_wakeup_capable(&pdev->dev, true);
> 
> > Maybe it makes sense to simply use device_init_wakeup here.
> 
> the explanation for device_init_wakeup
> 
> "By default, most devices should leave wakeup disabled. The exceptions
> are devices that everyone expects to be wakeup sources: keyboards, power
> buttons, ..."
> 
> made me think that device_set_wakeup_capable is more appropriate here. I
> can change this if you want.
> 

Doesn't everyone expect the RTC to be a wakeup source? :)

> However, if I compile rtc-imxdi as a module and use device_init_wakeup,
> the module can't be unloaded any more. The reason is that alarmtimer
> (kernel/time/alarmtimer.c) starts using rtc-imxdi as its backing rtc
> device and holds a reference to it. It seems that alarmtimer has no way
> to relinquish its backing rtc device, regardless of any pending alarms.
> 
> What is the right approach here? Are there any rtc drivers that act as a
> wakeup source and can still be unloaded if compiled as a module?
> 

Yes, when you don't have alarmtimer ;)
I honestly think the RTC selection needs to be a bit more dynamic but at
the same time, it would not be great to change it at suspend time. I
guess the best way would be to allow module unloading and tracking when
the RTC disappears.


-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com