I haven't looked at all the new clock/timer code, is there any utility in having support for more than one clock source?
Of course, you may register as many as you like.
Sure, but is there any utility in registering more than the decrementer on PPC?
Not yet. I'm not sure I know any other PPC CPU facility fitting for clockevents. In theory, FIT could be used -- but its period is measured in powers of 2, IIRC.
Wouldn't it be possible to use SoC timer functionality, too, and not limit
this to what is only present on the CPU die?
I guess the real question is, how high resolution does a high resolution
timer need to be,
The 52XX has 8 general purpose timers and 2 slice timers. Both will
generate an interrupt once the clock hits a preset value, the timing
of which is determined by prescalers and the IPB clock..