On Sun, 2022-05-01 at 23:48 +0100, Maciej W. Rozycki wrote: > On Fri, 29 Apr 2022, Niklas Schnelle wrote: > > > In a future patch HAS_IOPORT=n will result in inb()/outb() and friends > > not being declared. We thus need to add HAS_IOPORT as dependency for > > those drivers using them. It also turns out that with HAS_IOPORT handled > > explicitly HAMRADIO does not need the !S390 dependency and successfully > > builds the bpqether driver. > [...] > > diff --git a/drivers/net/fddi/Kconfig b/drivers/net/fddi/Kconfig > > index 846bf41c2717..fa3f1e0fe143 100644 > > --- a/drivers/net/fddi/Kconfig > > +++ b/drivers/net/fddi/Kconfig > > @@ -29,7 +29,7 @@ config DEFZA > > > > config DEFXX > > tristate "Digital DEFTA/DEFEA/DEFPA adapter support" > > - depends on FDDI && (PCI || EISA || TC) > > + depends on FDDI && (PCI || EISA || TC) && HAS_IOPORT > > help > > This is support for the DIGITAL series of TURBOchannel (DEFTA), > > EISA (DEFEA) and PCI (DEFPA) controllers which can connect you > > NAK, this has to be sorted out differently (and I think we discussed it > before). > > The driver works just fine with MMIO where available, so if `inb'/`outb' > do get removed, then only parts that rely on port I/O need to be disabled. > In fact there's already such provision there in drivers/net/fddi/defxx.c > for TURBOchannel systems (CONFIG_TC), which have no port I/O space either: > > #if defined(CONFIG_EISA) || defined(CONFIG_PCI) > #define dfx_use_mmio bp->mmio > #else > #define dfx_use_mmio true > #endif > > so I guess it's just the conditional that will have to be changed to: > > #ifdef CONFIG_HAS_IOPORT > > replacing the current explicit bus dependency list. The compiler will > then optimise away all the port I/O stuff (though I suspect dummy function > declarations may be required for `inb'/`outb', etc.). > > I can verify a suitable change with a TURBOchannel configuration once the > MIPS part has been sorted. > > Maciej With dfx_use_mmio changed as you propose above things compile on s390 which previously ran into missing (now __compile_error()) inl() via dfx_port_read_long() -> dfx_inl() -> inl(). Looking at the other uses of dfx_use_mmio I notice however that in dfx_get_bars(), inb() actually gets called when dfx_use_mmio is true. This happens if dfx_bus_eisa is also true. Now that variable is just the cached result of DFX_BUS_EISA(dev) which is defined to 0 if CONFIG_EISA is unset. I'm not 100% sure if going through a local variable is still considered trivial enough dead code elimination, at least it works for me™. I did also check the GCC docs and they explicitly say that __attribute__(error) is supposed to be used when dead code elimination gets rid of the error paths. I think we also need a "depends on HAS_IOPORT" for "config HAVE_EISA" just as I'm adding for "config ISA".
