Re: [PATCH 1/2] rtc: Add rtc_read_next_alarm() to read next expiring timer

[Ilpo Järvinen]

On Mon, 18 May 2026, Mario Limonciello wrote:
> On 5/18/26 11:48, Ilpo Järvinen wrote:
> > On Mon, 18 May 2026, Mario Limonciello wrote:
> > 
> > > Add a new function rtc_read_next_alarm() that reads the next expiring
> > > alarm from the RTC timerqueue. This is different from rtc_read_alarm(),
> > > which only reads the aie_timer.
> > > 
> > > The wakealarm sysfs file programs the rtc->aie_timer, whereas the
> > > alarmtimer suspend routine programs its own timer into the RTC timerqueue.
> > > Both timers end up in the RTC's timerqueue, and the first expiring timer
> > > is what gets armed in the hardware.
> > > 
> > > This new function allows code to query which alarm will actually fire
> > > next, regardless of which subsystem programmed it. This is needed by
> > > platform code that needs to program secondary timers based on the
> > > actual next wakeup time.
> > > 
> > > Link: https://lore.kernel.org/all/87ed50z0le.ffs@tglx
> > > Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > > Assisted-by: Claude:claude-opus-4-6
> > > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > > ---
> > >   drivers/rtc/interface.c | 42 +++++++++++++++++++++++++++++++++++++++++
> > >   include/linux/rtc.h     |  2 ++
> > >   2 files changed, 44 insertions(+)
> > > 
> > > diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
> > > index 1906f4884a834..dfcb32e272eb9 100644
> > > --- a/drivers/rtc/interface.c
> > > +++ b/drivers/rtc/interface.c
> > > @@ -384,6 +384,48 @@ int __rtc_read_alarm(struct rtc_device *rtc, struct
> > > rtc_wkalrm *alarm)
> > >   	return err;
> > >   }
> > >   +/**
> > > + * rtc_read_next_alarm - read the next expiring alarm
> > > + * @rtc: RTC device
> > > + * @alarm: storage for the alarm information
> > > + *
> > > + * Read the next expiring alarm from the RTC timerqueue. This returns
> > > + * the alarm that will actually fire next, which may be different from
> > > + * rtc_read_alarm() if multiple timers are queued (e.g., alarmtimer
> > > + * and wakealarm sysfs both active).
> > > + *
> > > + * Returns 0 on success, -ENOENT if no alarm is pending, or other error.
> > 
> > Missing :
> 
> Like this you mean, right?
> 
> Returns: 0 on success,..

Yes.

> > > + */
> > > +int rtc_read_next_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
> > > +{
> > > +	struct timerqueue_node *next;
> > > +	int err;
> > > +
> > > +	if (!rtc || !alarm)
> > > +		return -EINVAL;
> > > +
> > > +	err = mutex_lock_interruptible(&rtc->ops_lock);
> > > +	if (err)
> > > +		return err;
> > > +
> > > +	next = timerqueue_getnext(&rtc->timerqueue);
> > > +	if (!next) {
> > > +		err = -ENOENT;
> > > +		goto unlock;
> > > +	}
> > > +
> > > +	memset(alarm, 0, sizeof(struct rtc_wkalrm));
> > > +	alarm->time = rtc_ktime_to_tm(next->expires);
> > > +	alarm->enabled = 1;
> > > +	alarm->pending = 0;
> > 
> > Doesn't the preceeding memset() already clear everything?
> 
> Yeah; good point.
> 
> > 
> > > +	err = 0;
> > 
> > Why is this needed?
> 
> Oh I guess your point is that err was set to zero by
> mutex_lock_interruptible() already, so this is unecessary.
>
> Good catch, will drop it, thx.
> 
> > 
> > > +
> > > +unlock:
> > > +	mutex_unlock(&rtc->ops_lock);
> > > +	return err;
> > > +}
> > > +EXPORT_SYMBOL_GPL(rtc_read_next_alarm);
> > > +
> > >   int rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
> > >   {
> > >   	int err;
> > > diff --git a/include/linux/rtc.h b/include/linux/rtc.h
> > > index 95da051fb155d..c09fc22819d0c 100644
> > > --- a/include/linux/rtc.h
> > > +++ b/include/linux/rtc.h
> > > @@ -190,6 +190,8 @@ extern int rtc_set_time(struct rtc_device *rtc, struct
> > > rtc_time *tm);
> > >   int __rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm);
> > >   extern int rtc_read_alarm(struct rtc_device *rtc,
> > >   			struct rtc_wkalrm *alrm);
> > > +extern int rtc_read_next_alarm(struct rtc_device *rtc,
> > > +			       struct rtc_wkalrm *alrm);
> > >   extern int rtc_set_alarm(struct rtc_device *rtc,
> > >   				struct rtc_wkalrm *alrm);
> > >   extern int rtc_initialize_alarm(struct rtc_device *rtc,
> > > 
> > 
> 
> 

-- 
 i.