On Tue, 3 May 2022, Niklas Schnelle wrote: > > 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.). [...] > 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(). Great, thanks for checking! And I note referring `__compile_error' is roughly equivalent to a dummy declaration, so you've got that part sorted. > 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. Yeah, dead code elimination is supposed to handle such cases. The local automatic variable is essentially a syntactic feature not to use the same expression inline over and over throughout a function (for clarity the variable should probably be declared `const', but that is not essential) and it is up to the compiler whether to reuse the value previously calculated or to re-evaluate the expression. > I think we also need a "depends on HAS_IOPORT" for "config HAVE_EISA" > just as I'm adding for "config ISA". Oh absolutely! There's the slot-specific port I/O space that is used to identify EISA option cards in device discovery, so no EISA device will ever work without port I/O. Have a look at `decode_eisa_sig' in drivers/eisa/eisa-bus.c for the very obvious code. Note that some ISA cards can be configured to appear as EISA devices as well (I have a 3c509B Ethernet NIC set up that way). Maciej
