In both the 3.14.79-27-ARCH and 4.14 mainline kernels, we are now getting "hwclock: ioctl(3, RTC_UIE_ON, 0) to /dev/rtc0 failed: Invalid argument". Observed on multiple boards and multiple RTCs. This is a new issue within the past month.
Relevant link on odroid forum: https://forum.odroid.com/viewtopic.php?f=141&t=29173