On Fri, Nov 11, 2016 at 01:39:35PM +0000, Gabriele Paoloni wrote: > 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. Gabriele, > > 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 idea is a good one, however you are abusing PCIBIOS_MIN_IO and you actually need another variable for "reserving" an area in the I/O space that can be used for physical addresses rather than I/O tokens. The one good example for using PCIBIOS_MIN_IO is when your platform/architecture does not support legacy ISA operations *at all*. In that case someone sets the PCIBIOS_MIN_IO to a non-zero value to reserve that I/O range so that it doesn't get used. With Zhichang's patch you now start forcing those platforms to have a valid address below PCIBIOS_MIN_IO. For the general case you also have to bear in mind that PCIBIOS_MIN_IO could be zero. In that case, what is your "forbidden" range? [0, 0) ? So it makes sense to add a new #define that should only be defined by those architectures/ platforms that want to reserve on top of PCIBIOS_MIN_IO another region where I/O tokens can't be generated for. Best regards, Liviu > > > > > > > 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 -- ==================== | I would like to | | fix the world, | | but they're not | | giving me the | \ source code! / --------------- ¯\_(ツ)_/¯ -- 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
