There is one pSeries machine with a "real" serial port on it. I can't recall what it is.
The serial ports you see on the outside are connected to the FSP. There is then a communication path from the FSP via PHYP up to
AIX. This is ONLY for non-managed systems (no HMC). For managed systems, this path disappears.
Originally, the ports could not do anything but xon/xoff flow control. As far as I know, that has not changed. I don't think there is even a way to turn off flow control but I'm not 100% sure of that. And, other hardware characteristics like baudrate, bits per character, and parity are not controllable by
AIX. But I believe you can set all of them via the firmware ASMI menus. Again, I'm fairly sure about that but not 100% positive. (To recap, I am sure that
AIX can not set the hardware characteristics. I am not sure what options the ASMI menus provide.)
Having said all that, I would try it out. See if you can sweet talk it into working for you. Perhaps a consultant could help out. IBM will not "support" your configuration but perhaps in this case, the cost / benefit of that limitation is ok.
The cheapest alternative is the two port PCI adapter.
I don't know of any third party serial devices other than ethernet attached devices and you probably don't want to go that way.