On Wed, Jul 29, 2015 at 1:17 PM, Leo Yan [off-list ref] wrote:

This issue is found when i use file
kernel/power/suspend_test.c to verify the system suspend. Before the
system suspend, the flow need set 10's alarm in RTC for waken up
event.

But what i observed the phenomenon is:

At the init phase:
RTC_LR = 0x0;
RTC_DR = 0x0;
RTC_MR = 0x0;

According to the timeout is 10s, the function *pl031_set_alarm()* will
set RTC_MR = 10; So usually RTC_DR will increase one for every second
and will trigger interrupt when RTC_DR equal to RTC_MR. But on
Hi6220, though the RTC_DR init value is zero, but very soon it will be
set a random value which is bigger than 10.

Aha, that's annoying.

So it will never match with
RTC_MR register anymore; finally the system cannot resume back due the
waken up event will not be triggered.

OK I see.

So suspect RTC_LR has not been initailized correctly and it will load
random value to RTC_DR. After reset the RTC_LR, this issue will be
fixed.

quoted

quoted

+       /* Init registers */
+       writel(0x0, ldata->base + RTC_LR);

This will reset the clock to jan 1st 1970 on every reboot.
The idea is that the RTC should *preserve* the system time
if you reboot the system, so NACK.

Usually userspace has a script using hwclock to read the
system time from the rtc to system time with hwclock -s
after userspace comes up. Likewise it writes it back with
hwclock -w before rebooting.

This change is wrong.

I don't see what you mean here...

Most RTCs in the world have a battery back-up, so they
sustain time during shutdown. On an ARM system like this,
this PL031 derivative probably loose the time on shutdown,
but not on a soft reset.

However probe() will be called no matter if a shutdown or
soft reset happened, and the time will be reset to
1970-01-01 in any case with this change, even if it was
a soft reset and the time in the RTC is actually valid.

quoted

quoted

+       writel(RTC_BIT_AI, ldata->base + RTC_ICR);

So why do we want to have the alarm enabled by
default, before the kernel nor userspace has requested
it?

This is to clear any pending interrupt, but not enable alarm.

OK.

quoted

If your problem is with suspend/resume I suggest you work
on the [runtime]_suspend/resume hooks instead of probe().
Possibly you need to save/restore state across suspend/resume.

Do you think below change is make sense?

It's not using suspend/resume hooks but let's see...

+       /* Init registers */
+       writel(0x0, ldata->base + RTC_IMSC);
+       writel(RTC_BIT_AI, ldata->base + RTC_ICR);

Looks OK.

This badly needs a comment in the else-clause describing
what is happening here.

But I think it looks right! This will preserve the time across
soft reboots properly if I read it right.

Yours,
Linus Walleij