linux-kernel - Re: [PATCH 1/2] rtc-cmos: Clear expired alarm after resume

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Date:	Sat, 4 Jun 2016 19:48:54 +0200
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Gabriele Mazzotta <gabriele.mzt@...il.com>
Cc:	Alessandro Zummo <a.zummo@...ertech.it>,
	rtc-linux@...glegroups.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	matthew.garrett@...ula.com
Subject: Re: [PATCH 1/2] rtc-cmos: Clear expired alarm after resume

On 04/06/2016 at 18:58:59 +0200, Gabriele Mazzotta wrote :
> 2016-06-04 16:46 GMT+02:00 Alexandre Belloni
> <alexandre.belloni@...e-electrons.com>:
> > On 01/06/2016 at 17:40:14 +0200, Gabriele Mazzotta wrote :
> >> If the system wakes up because of a wake alarm, the internal state
> >> of the alarm is not updated. As consequence, the state no longer
> >> reflects the actual state of the hardware and setting a new alarm
> >> is not possible until the expired alarm is cleared.
> >>
> >
> > I'm not completely sure to understand what is happening but could you
> > check whether that one is solved by
> > 2b2f5ff00f63847d95adad6289bd8b05f5983dd5 in my tree (rtc-next).
> >
> 
> I picked 2b2f5ff00f63847d95adad6289bd8b05f5983dd5 and applied it
> on top of 4.7-rc1, but that didn't fix the problem.
> 
> Let me explain the problem by showing you how I reproduce it:
> 
> root@...alhost:~# cat /proc/driver/rtc | grep alarm_IRQ
> alarm_IRQ       : no
> root@...alhost:~# echo +10 > /sys/class/rtc/rtc0/wakealarm
> root@...alhost:~# echo mem > /sys/power/state  # wait for auto-resume
> root@...alhost:~# echo +10 > /sys/class/rtc/rtc0/wakealarm
> bash: echo: write error: Device or resource busy
> root@...alhost:~# cat /proc/driver/rtc | grep alarm_IRQ
> alarm_IRQ       : yes
> 
> To set another alarm, I have to first write 0 to wakealarm. After that
> I can set what I want. This doesn't happen if the alarm fires while
> the system is awake, it happens only if the system is suspended and
> the alarm wakes it.
> 
> I actually forgot to say that maybe this problem is not limited
> to rtc-cmos and that maybe a general solution could be used.
> 
> I've just looked better into what is causing this and the problem
> seems to be caused by the fact that rtc_timer_do_work() is not
> executed if the timer expires while the system is suspended.
> 

I doubt this is a driver independent issues as I don't get that
behaviour on many other RTCs. I'll have a look.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com