On Friday, November 18, 2016 4:18:07 PM CET Gabriele Paoloni wrote: > From: Arnd Bergmann [mailto:arnd@xxxxxxxx] > > On Friday, November 18, 2016 12:53:08 PM CET Gabriele Paoloni wrote: > > > From: Arnd Bergmann [mailto:arnd@xxxxxxxx] > > > > On Friday, November 18, 2016 12:07:28 PM CET Gabriele Paoloni > > > > The easiest change compared to the v5 code would be to walk > > > > a linked list of 'struct extio_ops' structures rather than > > > > assuming there is only ever one of them. I think one of the > > > > earlier versions actually did this. > > > > > > Right but if my understanding is correct if we live in a multi- > > > domain I/O space world when you have an input addr in the I/O > > > accessors this addr can be duplicated (for example for the standard > > > PCI IO domain and for our special LPC domain). > > > So effectively even if you walk a linked list there is a problem > > > of disambiguation...am I right? > > > > No, unlike the PCI memory space, the PIO addresses are not > > usually distinct, i.e. every PCI bus has its own 64K I/O > > addresses starting at zero. We linearize them into the > > Linux I/O space using the per-domain io_offset value. > > I am going to summarize my understanding here below: > > It seems to me that what is linearized is the virtual address > space associated to the IO address space. This address space > goes from PCI_IOBASE to (PCI_IOBASE + IO_SPACE_LIMIT). > > The I/O accessors perform rd/wr operation on this address > space using a port IO token. > > Each token map into a cpu physical address range > Each cpu physical address range maps to a bus address range > if the bus controller specifies a range property. > > Devices under a bus controller specify the bus addresses that > they operate on in their reg property. > > So each device can use the same bus addresses under two > separate bus controllers as long as the bus controller > use the range properties to map the same bus range to different > cpu address range. Sounds all correct to me so far, yes. > > For the ISA/LPC spaces there are only 4k of addresses, they > > the bus addresses always overlap, but we can trivially > > figure out the bus address from Linux I/O port number > > by subtracting the start of the range. > > Are you saying that our LPC controller should specify a > range property to map bus addresses into a cpu address range? No. There is not CPU address associated with it, because it's not memory mapped. Instead, we need to associate a bus address with a logical Linux port number, both in of_address_to_resource and in inb()/outb(). > > > > Another option the IA64 approach mentioned in another subthread > > > > today, looking up the operations based on an index from the > > > > upper bits of the port number. If we do this, we probably > > > > want to do that for all PIO access and replace the entire > > > > virtual address remapping logic with that. I think Bjorn > > > > in the past argued in favor of such an approach, while I > > > > advocated the current scheme for simplicity based on how > > > > every I/O space these days is just memory mapped (which now > > > > turned out to be false, both on powerpc and arm64). > > > > > > This seems really complex...I am a bit worried that possibly > > > we end up in having the maintainers saying that it is not worth > > > to re-invent the world just for this special LPC device... > > > > It would clearly be a rather invasive change, but the > > end-result isn't necessarily more complex than what we > > have today, as we'd kill off the crazy pci_pio_to_address() > > and pci_address_to_pio() hacks in address translation. > > I have to look better into this...can you provide me a reference > to the Bjorn argument in favor of this approach? The thread seems to have been pci: Introduce pci_register_io_range() helper function, e.g. in https://lkml.org/lkml/2014/7/8/969 > > > To be honest with you I would keep things simple for this > > > LPC and introduce more complex reworks later if more devices > > > need to be introduced. > > > > > > What if we stick on a single domain now where we introduce a > > > reserved threshold for the IO space (say INDIRECT_MAX_IO). > > > > I said having a single domain is fine, but I still don't > > like the idea of reserving low port numbers for this hack, > > it would mean that the numbers change for everyone else. > > I don't get this much...I/O tokens that are passed to the I/O > accessors are not fixed anyway and they vary depending on the order > of adding ranges to io_range_list...so I don't see a big issue > with this... On machines with a legacy devices behind the PCI bridge, there may still be a reason to have the low I/O port range reserved for the primary bus, e.g. to get a VGA text console to work. On powerpc, this is called the "primary" PCI host, i.e. the only one that is allowed to have an ISA bridge. Arnd -- 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
