I have a pair of Athlon64 machines that dual-boot 32-bit and
64-bit kernels. One annoying difference between the kernels
is that the PC Speaker driver (CONFIG_INPUT_PCSPKR=y) only
works in the 32-bit kernels. In the 64-bit kernels it remains
inactive and doesn't even generate any boot-time initialisation
or error messages.
Today I debugged that issue, and found that the PC Speaker
driver's ->probe() routine doesn't even get called in the
64-bit kernels. The reason for that is that the arch code
apparently has to explictly add a "pcspkr" platform device
in order for the driver core to call the ->probe() routine.
arch/i386/kernel/setup.c unconditionally adds a "pcspkr"
device, but the x86_64 kernel has no code at all related to
the PC Speaker.