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

[Mario Limonciello <mario.limonciello@amd.com>]

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@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 :

Like this you mean, right?

Returns: 0 on success,..

> 
>> + */
>> +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,
>>
>