On Wed, 2021-12-29 at 10:03 -0600, Bjorn Helgaas wrote: > On Wed, Dec 29, 2021 at 01:12:07PM +0100, Mauro Carvalho Chehab wrote: > > Em Wed, 29 Dec 2021 12:45:38 +0100 > > Niklas Schnelle <schnelle@xxxxxxxxxxxxx> escreveu: > > > ... > > > I do think we agree that once done correctly there is value in > > > such an option independent of HAS_IOPORT only gating inb() etc uses. > > I'm not sure I'm convinced about this. For s390, you could do this > patch series, where you don't define inb() at all, and you add new > dependencies to prevent compile errors. Or you could define inb() to > return ~0, which is what happens on other platforms when the device is > not present. > > > Personally, I don't see much value on a Kconfig var for legacy PCI I/O > > space. From maintenance PoV, bots won't be triggered if someone use > > HAS_IOPORT instead of the PCI specific one - or vice-versa. So, we > > could end having a mix of both at the wrong places, in long term. > > > > Also, assuming that PCIe hardware will some day abandon support for > > "legacy" PCI I/O space, I guess some runtime logic would be needed, > > in order to work with both kinds of PCIe controllers. So, having a > > Kconfig option won't help much, IMO. > > > > So, my personal preference would be to have just one Kconfig var, but > > I'm ok if the PCI maintainers decide otherwise. > > I don't really like the "LEGACY_PCI" Kconfig option. "Legacy" just > means something old and out of favor; it doesn't say *what* that > something is. > > I think you're specifically interested in I/O port space usage, and it > seems that you want all PCI drivers that *only* use I/O port space to > depend on LEGACY_PCI? Drivers that can use either I/O or memory > space or both would not depend on LEGACY_PCI? This seems a little > murky and error-prone. I'd like to hear Arnd's opinion on this but you're the PCI maintainer so of course your buy-in would be quite important for such an option. > > What if you used the approach from [1] but just dropped the warning? > The inb() would return ~0 if the platform doesn't support I/O port > space. Drivers should be prepared to handle that because that's what > happens if the device doesn't exist. Hmm, in that mail Linus very clearly and specifically asked for this to be a compile-time thing. So, if we do want to make it compile-time but keep the potential errors to a minimum I guess just having HAS_IOPORT might be valid compromise. It gets caught by bots through allyesconfig or randconfig on HAS_IOPORT=n architectures. Also it has a nice symmetry with the existing HAS_IOMEM. > > > HAS_IOPORT and LEGACY_PCI is a lot of Kconfiggery that basically just > avoids building drivers that aren't useful on s390. I'm not sure the > benefit outweighs the complication. > > Bjorn > > [1] https://lore.kernel.org/lkml/CAHk-=wg80je=K7madF4e7WrRNp37e3qh6y10Svhdc7O8SZ_-8g@xxxxxxxxxxxxxx/ > Despite s390 I believe it would also affect nds32, um, h8300, nios2, openrisc, hexagon, csky, and xtensa. But yes none of these is any less niche than us. I do wonder if we will see a new drivers using I/O ports?
