Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 4 May 2021 14:12:50 +0200
From:   Alexandre Belloni <alexandre.belloni@bootlin.com>
To:     Martin Kaiser <martin@kaiser.cx>
Cc:     Alessandro Zummo <a.zummo@towertech.it>,
        Shawn Guo <shawnguo@kernel.org>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>, linux-rtc@vger.kernel.org,
        linux-kernel@vger.kernel.org, Stephen Boyd <sboyd@kernel.org>
Subject: Re: [PATCH] rtc: imxdi: add wakeup support
Message-ID: <YJE6QhePvy7f4LKW@piout.net>
References: <20210430093210.7034-1-martin@kaiser.cx>
 <YI0n/7M3Ke4DAwG2@piout.net>
 <20210504100858.4i2crnfwchlcopr7@viti.kaiser.cx>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210504100858.4i2crnfwchlcopr7@viti.kaiser.cx>
Precedence: bulk

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