On Tuesday 08 July 2014, Bjorn Helgaas wrote: > On Tue, Jul 8, 2014 at 1:00 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Tuesday 08 July 2014, Bjorn Helgaas wrote: > >> On Tue, Jul 01, 2014 at 07:43:28PM +0100, Liviu Dudau wrote: > >> > +static LIST_HEAD(io_range_list); > >> > + > >> > +/* > >> > + * Record the PCI IO range (expressed as CPU physical address + size). > >> > + * Return a negative value if an error has occured, zero otherwise > >> > + */ > >> > +int __weak pci_register_io_range(phys_addr_t addr, resource_size_t size) > >> > >> I don't understand the interface here. What's the mapping from CPU > >> physical address to bus I/O port? For example, I have the following > >> machine in mind: > >> > >> HWP0002:00: PCI Root Bridge (domain 0000 [bus 00-1b]) > >> HWP0002:00: memory-mapped IO port space [mem 0xf8010000000-0xf8010000fff] > >> HWP0002:00: host bridge window [io 0x0000-0x0fff] > >> > >> HWP0002:09: PCI Root Bridge (domain 0001 [bus 00-1b]) > >> HWP0002:09: memory-mapped IO port space [mem 0xf8110000000-0xf8110000fff] > >> HWP0002:09: host bridge window [io 0x1000000-0x1000fff] (PCI address [0x0-0xfff]) > >> > >> The CPU physical memory [mem 0xf8010000000-0xf8010000fff] is translated by > >> the bridge to I/O ports 0x0000-0x0fff on PCI bus 0000:00. Drivers use, > >> e.g., "inb(0)" to access it. > >> > >> Similarly, [mem 0xf8110000000-0xf8110000fff] is translated by the second > >> bridge to I/O ports 0x0000-0x0fff on PCI bus 0001:00. Drivers use > >> "inb(0x1000000)" to access it. > > > > I guess you are thinking of the IA64 model here where you keep the virtual > > I/O port numbers in a per-bus lookup table that gets accessed for each > > inb() call. I've thought about this some more, and I believe there are good > > reasons for sticking with the model used on arm32 and powerpc for the > > generic OF implementation. > > > > The idea is that there is a single virtual memory range for all I/O port > > mappings and we use the MMU to do the translation rather than computing > > it manually in the inb() implemnetation. The main advantage is that all > > functions used in device drivers to (potentially) access I/O ports > > become trivial this way, which helps for code size and in some cases > > (e.g. SoC-internal registers with a low latency) it may even be performance > > relevant. > > My example is from ia64, but I'm not advocating for the lookup table. > The point is that the hardware works similarly (at least for dense ia64 > I/O port spaces) in terms of mapping CPU physical addresses to PCI I/O > space. > > I think my confusion is because your pci_register_io_range() and > pci_addess_to_pci() implementations assume that every io_range starts at > I/O port 0 on PCI (correct me if I'm wrong). I suspect that's why you > don't save the I/O port number in struct io_range. I think you are just misreading the code, but I agree it's hard to understand and I made the same mistake in my initial reply to the first version. pci_register_io_range and pci_address_to_pci only worry about the mapping between CPU physical and Linux I/O address, they do not care which PCI port numbers are behind that. The mapping between PCI port numbers and Linux port numbers is done correctly in patch 8/9 in the pci_host_bridge_of_get_ranges() function. > Maybe that assumption is guaranteed by OF, but it doesn't hold for ACPI; > ACPI can describe several I/O port apertures for a single bridge, each > associated with a different CPU physical memory region. DT can have the same, although the common case is that each PCI host bridge has 64KB of I/O ports starting at address 0. Most driver writers get it wrong for the case where it starts at a different address, so I really want to have a generic implementation that gets it right. > If my speculation here is correct, a comment to the effect that each > io_range corresponds to a PCI I/O space range that starts at 0 might be > enough. > > If you did add a PCI I/O port number argument to pci_register_io_range(), > we might be able to make an ACPI-based implementation of it. But I guess > that could be done if/when anybody ever wants to do that. I think we shoulnd't worry about it before we actually need it. As far as I understand, the only user of that code (unless someone wants to convert ia64) would be ARM64 with ACPI, but that uses the SBSA hardware model that recommends having no I/O space at all. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
