On Thu, 2021-12-30 at 16:44 +1300, Michael Schmitz wrote: > Hi Arnd, > > Am 30.12.2021 um 14:48 schrieb Arnd Bergmann: > > On Tue, Dec 28, 2021 at 11:15 PM Michael Schmitz <schmitzmic@xxxxxxxxx> wrote: > > > Am 29.12.2021 um 16:41 schrieb Arnd Bergmann: > > > > On Tue, Dec 28, 2021 at 8:20 PM Michael Schmitz <schmitzmic@xxxxxxxxx> wrote: ---8<--- > > > What some other architectures do is to rely on inb()/outb() to have a > > zero-based offset, and use an io_offset in PCI buses to ensure that a > > low port number on the bus gets translated into a pointer value for the > > virtual mapping in the kernel, which is then represented as an unsigned > > int. > > M54xx does just that for Coldfire: > > arch/m68k/include/asm/io_no.h: > #define PCI_IO_PA 0xf8000000 /* Host physical address */ > > (used to set PCI BAR mappings, so matches your definition above). > > All other (MMU) m68k users of inb()/outb() apply an io_offset in the > platform specific address translation: > > ---8<--- > So as long as support for any of the m68k PCI or ISA bridges is selected > in the kernel config, the appropriate IO space mapping is applied. If no > support for PCI or ISA bridges is selected, we already fall back to zero > offset mapping (but as far as I can tell, it shouldn't be possible to > build a kernel without bridge support but drivers that require it). > > > As this is indistinguishable from architectures that just don't have > > a base address for I/O ports (we unfortunately picked 0 as the default > > PCI_IOBASE value), my suggestion was to start marking architectures > > that may have this problem as using HAS_IOPORT in order to keep > > the existing behavior unchanged. If m68k does not suffer from this, > > making HAS_IOPORT conditional on those config options that actually > > need it would of course be best. > > Following your description, HAS_IOPORT would be required for neither of > PCI, ISA or ATARI_ROM_ISA ?? > No, HAS_IOPORT being set just means that inb() etc. exist and are functional be it as special instructions like on x86 or via an I/O address offset. As I understand it if you do have PCI, ISA or ATARI_ROM_ISA they are functional. If none of them are set and your zero offset mapping means these accessors can't actually be used you could make the declerations ifdeffed on CONFIG_HAS_IOPORT to detect the cases where somone managed to build drivers that require them and that would result in a compile time error instead of silently, or with a NULL pointer warning, compiling code that won't work.
