linux-kernel - Re: [PATCH] rtc: imxdi: add wakeup support

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Date:   Tue, 4 May 2021 14:12:50 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Martin Kaiser <martin@...ser.cx>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Shawn Guo <shawnguo@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Stephen Boyd <sboyd@...nel.org>
Subject: Re: [PATCH] rtc: imxdi: add wakeup support

On 04/05/2021 12:08:58+0200, Martin Kaiser wrote:
> Thus wrote Alexandre Belloni (alexandre.belloni@...tlin.com):
> 
> > >  	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