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

From: Gabriele Mazzotta
Date: Sat Jun 04 2016 - 12:59:19 EST

2016-06-04 16:46 GMT+02:00 Alexandre Belloni
> Hi,
> 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@localhost:~# cat /proc/driver/rtc | grep alarm_IRQ
alarm_IRQ : no
root@localhost:~# echo +10 > /sys/class/rtc/rtc0/wakealarm
root@localhost:~# echo mem > /sys/power/state # wait for auto-resume
root@localhost:~# echo +10 > /sys/class/rtc/rtc0/wakealarm
bash: echo: write error: Device or resource busy
root@localhost:~# 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.

The following solves this particular problem:

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 74fd974..80d6a12 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -102,6 +102,9 @@ static int rtc_resume(struct device *dev)
struct timespec64 sleep_time;
int err;

+ /* A timer might have expired while suspended */
+ schedule_work(&rtc->irqwork);
if (timekeeping_rtc_skipresume())
return 0;

> --
> Alexandre Belloni, Free Electrons
> Embedded Linux, Kernel and Android engineering