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

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

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@linutronix.de>
> Assisted-by: Claude:claude-opus-4-6
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
>  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 :

> + */
> +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?

> +	err = 0;

Why is this needed?

> +
> +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.