On Tue, Nov 08, 2016 at 05:19:54PM +0100, Arnd Bergmann wrote: > On Tuesday, November 8, 2016 11:49:53 AM CET Mark Rutland wrote: > > My understanding of ISA (which may be flawed) is that it's not part of > > the PCI host bridge, but rather on x86 it happens to share the IO space > > with PCI. > > On normal systems, ISA or LPC are behind a PCI bridge device, which > passes down both low addresses of I/O space and memory space. Ok, so the use of those address spaces is an artifact of the ISA controller being a device under the PCI host bridge. Given we can have multiple domains, surely that implies we can have multiple ISA controllers in general? > > I believe that we could theoretically have multiple independent LPC/ISA > > busses, as is possible with PCI on !x86 systems. If the current ISA code > > assumes a singleton bus, I think that's something that needs to be fixed > > up more generically. > > > > I don't see why we should need any architecture-specific code here. Why > > can we not fix up the ISA bus code in drivers/of/address.c such that it > > handles multiple ISA bus instances, and translates all sub-device > > addresses relative to the specific bus instance? > > I think it is a relatively safe assumption that there is only one > ISA bridge. A lot of old drivers hardcode PIO or memory addresses > when talking to an ISA device, so having multiple instances is > already problematic. I'm worried that this might not be a safe assumption. Hardware these days has a habit of pushing the boundaries of our expectations. If we're going to assume that, I'd certainly want the kernel to verify that it's true for all instanciated ISA/LPC devices. Otherwise, I can imagine people relying on (or working around) that assumption in ACPI tables and DTs, and that will be a nightmare (at best) to untangle in future. Thanks, Mark. -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
