Real Time Clock

modulename: rtc-core.ko

configname: CONFIG_RTC_CLASS

Linux Kernel Configuration
└─>Device Drivers
└─>Real Time Clock
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
Generic RTC class support. If you say yes here, you will
be allowed to plug one or more RTCs to your system. You will
probably want to enable one or more of the interfaces below.

source code:
drivers/rtc/
selects
CONFIG_RTC_LIB

depends
NOT CONFIG_S390
NOT CONFIG_UML