I have a config from a 32-bit linux 3.12.18, and was trying to compile a 64 bit version with most settings like selected drivers etc. the same as in 32 bit version. For this I used
make menuconfig with
.config in source tree, and checked "64 bit kernel". After installation I rebooted with this shiny new kernel, and everything worked... well almost everything. For some reason I appeared to not have
/dev/rtc*, which was present on 32 bit kernel, and of course
hwclock utility didn't work, while it worked on 32 bits.
I've spend some time trying to figure out what the difference is, and found that the whole
CONFIG_RTC_CLASS thing with its children was just not mentioned in 32-bit
.config and set as
is not set in 64 bit version. So it looks like the kernel's default config regarding RTC is different in 32 and 64 bit compilation modes.
Why such a difference? Is PC RTC normally superseded by something else on modern 64 bit systems, or what?