On Wed, May 04, 2022 at 03:24:39PM +0100, Maciej W. Rozycki wrote: > On Wed, 4 May 2022, Arnd Bergmann wrote: > > > > POWER9 is another architecture with no port I/O space[1]: > > > > POWER9 is just an implementation of the power architecture > > that has a particular PCI host bridge. I would assume that > > arch/powerpc/ would continue to set HAS_IOPORT because > > it knows how to access I/O ports at compile-time. > > Well, yes, except I would expect POWER9_CPU (and any higher versions we > eventually get) to clear HAS_IOPORT. Generic configurations (GENERIC_CPU) > would set HAS_IOPORT of course, as would any lower architecture variants > that do or may support port I/O (it's not clear to me if there are any > that do not). Ideally a generic configuration would not issue accesses to > random MMIO locations for port I/O accesses via `inb'/`outb', etc. for > systems that do not support port I/O (which it now does, or at least used > to until recently). It would seem weird to me that a module would build and run on a generic kernel running on POWER9 (with some safe way of handling inb/outb that don't actually work), but not on a kernel built specifically for POWER9_CPU. It sounds like inb/outb in a generic kernel on POWER9 may not currently do something sensible, but that's fixable, e.g., make inb() return 0xff and outb() a no-op. I would naively expect the same behavior in a POWER9_CPU kernel. Bjorn
