Hi Arnd many thanks for your help here > -----Original Message----- > From: Arnd Bergmann [mailto:arnd@xxxxxxxx] > Sent: 18 November 2016 10:18 > To: liviu.dudau@xxxxxxx > Cc: Gabriele Paoloni; 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; bhelgaas@go ogle.com; > zhichang.yuan02@xxxxxxxxx; Jason Gunthorpe; Thomas Petazzoni > Subject: Re: [PATCH V5 3/3] ARM64 LPC: LPC driver implementation on > Hip06 > > On Monday, November 14, 2016 11:26:25 AM CET liviu.dudau@xxxxxxx wrote: > > On Mon, Nov 14, 2016 at 08:26:42AM +0000, Gabriele Paoloni wrote: > > > > Nope, that is not what it means. It means that PCI devices can > see I/O > > > > addresses > > > > on the bus that start from 0. There never was any usage for non- > PCI > > > > controllers > > > > > > So I am a bit confused... > > > From http://www.firmware.org/1275/bindings/isa/isa0_4d.ps > > > It seems that ISA buses operate on cpu I/O address range [0, > 0xFFF]. > > > I thought that was the reason why for most architectures we have > > > PCIBIOS_MIN_IO equal to 0x1000 (so I thought that ISA controllers > > > usually use [0, PCIBIOS_MIN_IO - 1] ) > > > > First of all, cpu I/O addresses is an x86-ism. ARM architectures and > others > > have no separate address space for I/O, it is all merged into one > unified > > address space. So, on arm/arm64 for example, PCIBIOS_MIN_IO = 0 could > mean > > that we don't care about ISA I/O because the platform does not > support having > > an ISA bus (e.g.). > > I think to be more specific, PCIBIOS_MIN_IO=0 would indicate that you > cannot > have a PCI-to-ISA or PCI-to-LPC bridge in any PCI domain. This is > different > from having an LPC master outside of PCI, as that lives in its own > domain > and has a separately addressable I/O space. Yes correct so if we go for the single domain solution arch that have PCIBIOS_MIN_IO=0 cannot support special devices such as LPC unless we also redefine PCIBIOS_MIN_IO, right? > > > > As said before this series forbid IO tokens to be in [0, > PCIBIOS_MIN_IO) > > > to allow special ISA controllers to use that range with special > > > accessors. > > > Having a variable threshold would make life much more difficult > > > as there would be a probe dependency between the PCI controller and > > > the special ISA one (PCI to wait for the special ISA device to be > > > probed and set the right threshold value from DT or ACPI table). > > > > > > Instead using PCIBIOS_MIN_IO is easier and should not impose much > > > constraint as [PCIBIOS_MIN_IO, IO_SPACE_LIMIT] is available to > > > the PCI controller for I/O tokens... > > > > What I am suggesting is to leave PCIBIOS_MIN_IO alone which still > reserves > > space for ISA controller and add a PCIBIOS_MIN_DIRECT_IO that will > reserve > > space for your direct address I/O on top of PCIBIOS_MIN_IO. > > The PCIBIOS_MIN_DIRECT_IO name still suggests having something related > to > PCIBIOS_MIN_IO, but it really isn't. We are talking about multiple > concepts here that are not the same but that are somewhat related: > > a) keeping PCI devices from allocating low I/O ports on the PCI bus > that would conflict with ISA devices behind a bridge of the > same bus. > > b) reserving the low 0x0-0xfff range of the Linux-internal I/O > space abstraction to a particular LPC or PCI domain to make > legacy device drivers work that hardcode a particular port > number. > > c) Redirecting inb/outb to call a domain-specific accessor function > rather than doing the normal MMIO window for an LPC master or > more generally any arbitrary LPC or PCI domain that has a > nonstandard I/O space. > [side note: actually if we generalized this, we could avoid > assigning an MMIO range for the I/O space on the pci-mvebu > driver, and that would help free up some other remapping > windows] > > 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? Thanks Gab > > 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
