Yes, I see now that P2 is the VideoCore JTAG only and not for debugging.
There is this comment on coder27s link:
It is also possible to reconfigure GPIO connector pins P1-7, 15, 16, 18, 22 (chipset GPIOs 4 and 22 to 25) to provide an ARM JTAG interface.[11] However ARM_TMS isn't available on the GPIO connector (chipset pin 12 or 27 is needed).
Unfortunately, the given link [11] appears to be broken or at least doesn't take you directly to the information.
