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 wrote: > > > > I think there is no need to change a) here, we have PCIBIOS_MIN_IO > > > > today and even if we don't need it, there is no obvious downside. > > > > I would also argue that we can ignore b) for the discussion of > > > > the HiSilicon LPC driver, we just need to assign some range > > > > of logical addresses to each domain. > > > > > > > > That means solving c) is the important problem here, and it > > > > shouldn't be so hard. We can do this either with a single > > > > special domain as in the v5 patch series, or by generalizing it > > > > so that any I/O space mapping gets looked up through the device > > > > pointer of the bus master. > > > > > > I am not very on the "generalized" multi-domain solution... > > > Currently the IO accessors prototypes have an unsigned long addr > > > as input parameter. If we live in a multi-domain IO system > > > how can we distinguish inside the accessor which domain addr > > > belongs to? > > > > 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. 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. > > 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. > 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. > We define INDIRECT_MAX_IO as 0 in "include/linux/extio.h" and > we define INDIRECT_MAX_IO as 0x1000 in "arch/arm64/include/asm/io.h" > > So effectively this threshold can change according to the > architecture and so far we only define it for ARM64 as we need > it for ARM64... I liked the idea of having it done in asm-generic/io.h (in an ifdef) and lib/*.c under an as someone suggested earlier. There is nothing ARM64 specific in the implementation. 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
