Re: [PATCH 1/1] tty: serial: handle HAS_IOPORT dependencies

[Maciej W. Rozycki]

Hi Niklas,

> With 2 more HAS_IOPORT patches having gone into v6.12-rc1 I'm looking
> at what's left and we're down to 4 prerequisite patches[0] before being
> able to compile-time disable inb()/outb()/…. This one being by far the
> largest of these. Looking at your suggestion it seems that to compile
> 8250_pci.c without HAS_IOPORT I'll have to add #ifdef CONFIG_HAS_IOPORT
> around the MOXI section as that uses I/O ports unconditionally. The
> rest seems fine and I guess would theoretically work on a system with
> !HAS_IOPORT. I'll send a v2 with that included. 

 I've skimmed over and I agree, though I'd place some of the #ifdefs 
differently, e.g. above #define QPCR_TEST_FOR1.  Overall I think it would 
make sense to reorder code and group stuff that depends on port I/O such 
as to minimise the number of #ifdefs.

 Ideally we could come with a slightly user-friendlier change that would 
report the inability to handle port I/O devices as they are discovered 
rather than just silently ignoring them.

> Note however that even though your POWER9 system does not have I/O port
> support in hardware we still have HAS_IOPORT enabled for arch/powerpc
> if PCI is enabed so even with this patch as is your POWER9 system
> should not be affected.

 I think we need to get this right regardless.  And also while I run a 
generic distribution kernel on my POWER9 as a production system, I'd love 
to see an option to build a tailored configuration that would indeed 
remove support for port I/O from the kernel side for systems like mine 
that have no provision for port I/O in hardware, knowing that such a 
kernel will only ever run on such hardware and discarding compiled code 
that won't ever be used.

  Maciej