Re: [Question] rtc wake behavior and sysfs

[Alexandre Belloni]

On 05/10/2020 09:13:08-0400, Peter Geis wrote:
> Good Morning,
> 
> While testing suspend to ram on the Ouya, I encountered an interesting
> issue with the rtc-tps65910 driver.
> Attempting to use rtc-wake on the default configuration returned:
> rtcwake: /dev/rtc0 not enabled for wakeup events
> This is due to:
> eb5eba4ef722 drivers/rtc/rtc-tps65910.c: enable/disable wake in suspend/resume
> This commit changed this driver's behavior to not enable wakeup by
> default, but enables it when entering sleep mode.
> This seems to be odd behavior to me.
> Looking at a few other rtc drivers show they simply enable themselves
> as wakeup sources by default.
> 
> I also found the sysfs entries are at /sys/devices/ ..
> /tps65910-rtc/power but are missing at /sys/class/rtc/rtc0/power/
> 
> I have two questions.
>  - Should the sysfs wakeup entries be missing at /sys/class/rtc/rtc0/power/ ?

I would be in /sys/class/rtc/rtc0/device/power

>  - Shouldn't a rtc be enabled as a wakeup source by default?
> 

The short answer is no, the reason being that not all RTCs are connected
to an IRQ or a pin that can wakeup or start the platform. What should be
done is enabling wakeup only when interrupts are available or the
wakeup-source property is in the rtc device tree node.

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