Re: [REGRESSION] rtc/interface.c: kills suspend-to-ram

From: John Stultz
Date: Tue Apr 17 2012 - 01:14:03 EST

On 04/16/2012 07:30 PM, Mark Lord wrote:

Thanks for looking into it, John.

I also spent many more hours digging away at it here today,
and I now understand (mostly) what is happening and why.

The code above introduces a new access to the RTC that never existed before.
For the case where the Alarm has never been enabled by software,
I believe the code above will still try to "disable" it.
That's the new behaviour we didn't have prior to this patch.

And.. on some of the systems I'm testing on, the BIOS setup has
the RTC Alarm "enabled", which means "under BIOS control",
as opposed to "disabled" which means "under software control".

It's the "under BIOS control" systems that the above patch breaks.

So I think the code may just need to be slightly more clever,
and not disable an Alarm that was never enabled by software in the first place.

Thanks for the extra info. Although I'm still a little perplexed why that's causing trouble.
When "under BIOS control" is the RTC unusable by the kernel? Will any access cause problems? Or just the extra disable path?

On a hunch, I wonder if your tripping over the alarmtimer initialization issue that was recently fixed.
Have you also seen this issue w/ 3.4-rc2+ ?

I still can't trigger anything similar playing with the BIOS options for my system. If its not too much trouble, could you try the following two changes?


I guess I'm curious why you're hitting the rtc_alarm_disable if you're not using the alarm. If you use the following diff, can you provide the resulting stack traces?

diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index eb415bd..4c98ee5 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -786,7 +786,8 @@ static void rtc_alarm_disable(struct rtc_device *rtc)
if (!rtc->ops || !rtc->ops->alarm_irq_enable)

- rtc->ops->alarm_irq_enable(rtc->dev.parent, false);
+ //rtc->ops->alarm_irq_enable(rtc->dev.parent, false);
+ dump_stack();


Then un-comment/re-add the alarm_irq_enable() call above, and try the following, to see if the behavior changes? Then re-add each line one by one to see if you can isolate where things go wrong in the cmos code?

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index 7d5f56e..c500bce 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -318,9 +318,9 @@ static void cmos_irq_disable(struct cmos_rtc *cmos, unsigned char mask)
rtc_control = CMOS_READ(RTC_CONTROL);
rtc_control&= ~mask;
- hpet_mask_rtc_irq_bit(mask);
+ //hpet_mask_rtc_irq_bit(mask);

- cmos_checkintr(cmos, rtc_control);
+ //cmos_checkintr(cmos, rtc_control);

static int cmos_set_alarm(struct device *dev, struct rtc_wkalrm *t)

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