Peter Maydell <peter.maydell@xxxxxxxxxx> writes: > On 30 January 2013 11:39, Andreas Färber <afaerber@xxxxxxx> wrote: >> Proposal by hpoussin was to move _list_add() code to ISADevice: >> http://lists.gnu.org/archive/html/qemu-devel/2013-01/msg00508.html >> >> Concerns: >> * PCI devices (VGA, QXL) register I/O ports as well >> => above patches add dependency on ISABus to machines >> -> "<benh> no mac ever had one" >> => PCIDevice shouldn't use ISA API with NULL ISADevice >> * Lack of avi: Who decides about memory API these days? >> >> armbru and agraf concluded that moving this into ISA is wrong. >> >> => I will drop the remaining ioport patches from above series. >> >> Suggestions on how to proceed with tackling the issue are welcome. > > How does this stuff work on real hardware? I would have > expected that a PCI device registering the fact it has > IO ports would have to do so via the PCI controller it > is plugged into... > > My naive don't-know-much-about-portio suggestion is that this > should work the same way as memory regions: each device > provides portio regions, and the controller for the bus > (ISA or PCI) exposes those to the next layer up, and > something at board level maps it all into the right places. Makes sense me, but I'm naive, too :) For me, "I/O ports" are just an alternate address space some devices have. For instance, x86 CPUs have an extra pin for selecting I/O vs. memory address space. The ISA bus has separate read/write pins for memory and I/O. This isn't terribly special. Mapping address spaces around is what devices bridging buses do. I'd expect a system bus for an x86 CPU to have both a memory and an I/O address space. I'd expect an ISA PC's sysbus - ISA bridge to map both directly. I'd expect an ISA bridge for a sysbus without a separate I/O address space to map the ISA I/O address space into the sysbus's normal address space somehow. PCI ISA bridges have their own rules, but I've gotten away with ignoring the details so far :) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
