Hi Arnd > -----Original Message----- > From: Arnd Bergmann [mailto:arnd@xxxxxxxx] > Sent: 10 November 2016 16:07 > To: Gabriele Paoloni > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; Yuanzhichang; > mark.rutland@xxxxxxx; devicetree@xxxxxxxxxxxxxxx; > lorenzo.pieralisi@xxxxxxx; minyard@xxxxxxx; linux-pci@xxxxxxxxxxxxxxx; > benh@xxxxxxxxxxxxxxxxxxx; John Garry; will.deacon@xxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx; xuwei (O); Linuxarm; zourongrong@xxxxxxxxx; > robh+dt@xxxxxxxxxx; kantyzc@xxxxxxx; linux-serial@xxxxxxxxxxxxxxx; > catalin.marinas@xxxxxxx; olof@xxxxxxxxx; liviu.dudau@xxxxxxx; > bhelgaas@googl e.com; zhichang.yuan02@xxxxxxxxx > Subject: Re: [PATCH V5 3/3] ARM64 LPC: LPC driver implementation on > Hip06 > > On Thursday, November 10, 2016 3:36:49 PM CET Gabriele Paoloni wrote: > > > > Where should we get the range from? For LPC we know that it is going > > Work on anything that is not used by PCI I/O space, and this is > > why we use [0, PCIBIOS_MIN_IO] > > It should be allocated the same way we allocate PCI config space > segments. This is currently done with the io_range list in > drivers/pci/pci.c, which isn't perfect but could be extended > if necessary. Based on what others commented here, I'd rather > make the differences between ISA/LPC and PCI I/O ranges smaller > than larger. I am not sure this would make sense... IMHO all the mechanism around io_range_list is needed to provide the "mapping" between I/O tokens and physical CPU addresses. Currently the available tokens range from 0 to IO_SPACE_LIMIT. As you know the I/O memory accessors operate on whatever __of_address_to_resource sets into the resource (start, end). With this special device in place we cannot know if a resource is assigned with an I/O token or a physical address, unless we forbid the I/O tokens to be in a specific range. So this is why we are changing the offsets of all the functions handling io_range_list (to make sure that a range is forbidden to the tokens and is available to the physical addresses). We have chosen this forbidden range to be [0, PCIBIOS_MIN_IO) because this is the maximum physical I/O range that a non PCI device can operate on and because we believe this does not impose much restriction on the available I/O token range; that now is [PCIBIOS_MIN_IO, IO_SPACE_LIMIT]. So we believe that the chosen forbidden range can accommodate any special ISA bus device with no much constraint on the rest of I/O tokens... > > > > Your current version has > > > > > > if (arm64_extio_ops->pfout) \ > > > arm64_extio_ops->pfout(arm64_extio_ops->devpara,\ > > > addr, value, sizeof(type)); \ > > > > > > Instead, just subtract the start of the range from the logical > > > port number to transform it back into a bus-local port number: > > > > These accessors do not operate on IO tokens: > > > > If (arm64_extio_ops->start > addr || arm64_extio_ops->end < addr) > > addr is not going to be an I/O token; in fact patch 2/3 imposes that > > the I/O tokens will start at PCIBIOS_MIN_IO. So from 0 to > PCIBIOS_MIN_IO > > we have free physical addresses that the accessors can operate on. > > Ah, I missed that part. I'd rather not use PCIBIOS_MIN_IO to refer to > the logical I/O tokens, the purpose of that macro is really meant > for allocating PCI I/O port numbers within the address space of > one bus. As I mentioned above, special devices operate on CPU addresses directly, not I/O tokens. For them there is no way to distinguish.... > > Note that it's equally likely that whichever next platform needs > non-mapped I/O access like this actually needs them for PCI I/O space, > and that will use it on addresses registered to a PCI host bridge. Ok so here you are talking about a platform that has got an I/O range under the PCI host controller, right? And this I/O range cannot be directly memory mapped but needs special redirections for the I/O tokens, right? In this scenario registering the I/O ranges with the forbidden range implemented by the current patch would still allow to redirect I/O tokens as long as arm64_extio_ops->start >= PCIBIOS_MIN_IO So effectively the special PCI host controller 1) knows the physical range that needs special redirection 2) register such range 3) uses pci_pio_to_address() to retrieve the IO tokens for the special accessors 4) sets arm64_extio_ops->start/end to the IO tokens retrieved in 3) So to be honest I think this patch can fit well both with special PCI controllers that need I/O tokens redirection and with special non-PCI controllers that need non-PCI I/O physical address redirection... Thanks (and sorry for the long reply but I didn't know how to make the explanation shorter :) ) Gab > > If we separate the two steps: > > a) assign a range of logical I/O port numbers to a bus > b) register a set of helpers for redirecting logical I/O > port to a helper function > > then I think the code will get cleaner and more flexible. > It should actually then be able to replace the powerpc > specific 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
