From: Linuxppc-dev Arnd Bergmann > Sent: 05 April 2023 21:32 > > On Wed, Apr 5, 2023, at 22:00, H. Peter Anvin wrote: > > On April 5, 2023 8:12:38 AM PDT, Niklas Schnelle <schnelle@xxxxxxxxxxxxx> wrote: > >>On Thu, 2023-03-23 at 17:33 +0100, Niklas Schnelle wrote: > >>> We introduce a new HAS_IOPORT Kconfig option to indicate support for I/O > >>> Port access. In a future patch HAS_IOPORT=n will disable compilation of > >>> the I/O accessor functions inb()/outb() and friends on architectures > >>> which can not meaningfully support legacy I/O spaces such as s390. > >>> >> > >>Gentle ping. As far as I can tell this hasn't been picked to any tree > >>sp far but also hasn't seen complains so I'm wondering if I should send > >>a new version of the combined series of this patch plus the added > >>HAS_IOPORT dependencies per subsystem or wait until this is picked up. > > > > You need this on a system supporting not just ISA but also PCI. > > > > Typically on non-x86 architectures this is simply mapped into a memory window. > > I'm pretty confident that the list is correct here, as the HAS_IOPORT > symbol is enabled exactly for the architectures that have a way to > map the I/O space. PCIe generally works fine without I/O space, the > only exception are drivers for devices that were around as early PCI. Isn't there a difference between cpu that have inb()/outb() (probably only x86?) and architectures (well computer designs) that can generate PCI 'I/O' cycles by some means. It isn't even just PCI I/O cycles, I've used an ARM cpu (SA1100) that mapped a chuck of physical address space onto PCMCIA I/O cycles. If the hardware can map a PCI 'IO' bar into normal kernel address space then the bar and accesses can be treated exactly like a memory bar. This probably leaves x86 as the outlier where you need (IIRC) io_readl() and friends that can generate in/out instructions for those accesses. There are also all the x86 ISA devices which need in/out instructions. But (with the likely exception of the UART) they are pretty much platform specific. So, to my mind at least, HAS_IOPORT is just the wrong question. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
