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    SubjectRe: [PATCH v5 04/12] PCI: brcmstb: add dma-range mapping for inbound traffic
    On Thu, Sep 20, 2018 at 5:39 PM Florian Fainelli <f.fainelli@gmail.com> wrote:
    >
    > On 09/20/2018 02:33 PM, Ard Biesheuvel wrote:
    > > On 20 September 2018 at 14:31, Florian Fainelli <f.fainelli@gmail.com> wrote:
    > >> On 09/20/2018 02:04 PM, Ard Biesheuvel wrote:
    > >>> On 20 September 2018 at 13:55, Florian Fainelli <f.fainelli@gmail.com> wrote:
    > >>>> On 09/19/2018 07:19 PM, Ard Biesheuvel wrote:
    > >>>>> On 19 September 2018 at 07:31, Jim Quinlan <jim2101024@gmail.com> wrote:
    > >>>>>> The Broadcom STB PCIe host controller is intimately related to the
    > >>>>>> memory subsystem. This close relationship adds complexity to how cpu
    > >>>>>> system memory is mapped to PCIe memory. Ideally, this mapping is an
    > >>>>>> identity mapping, or an identity mapping off by a constant. Not so in
    > >>>>>> this case.
    > >>>>>>
    > >>>>>> Consider the Broadcom reference board BCM97445LCC_4X8 which has 6 GB
    > >>>>>> of system memory. Here is how the PCIe controller maps the
    > >>>>>> system memory to PCIe memory:
    > >>>>>>
    > >>>>>> memc0-a@[ 0....3fffffff] <=> pci@[ 0....3fffffff]
    > >>>>>> memc0-b@[100000000...13fffffff] <=> pci@[ 40000000....7fffffff]
    > >>>>>> memc1-a@[ 40000000....7fffffff] <=> pci@[ 80000000....bfffffff]
    > >>>>>> memc1-b@[300000000...33fffffff] <=> pci@[ c0000000....ffffffff]
    > >>>>>> memc2-a@[ 80000000....bfffffff] <=> pci@[100000000...13fffffff]
    > >>>>>> memc2-b@[c00000000...c3fffffff] <=> pci@[140000000...17fffffff]
    > >>>>>>
    > >>>>>
    > >>>>> So is describing this as
    > >>>>>
    > >>>>> dma-ranges = <0x0 0x0 0x0 0x0 0x0 0x40000000>,
    > >>>>> <0x0 0x40000000 0x1 0x0 0x0 0x40000000>,
    > >>>>> <0x0 0x80000000 0x0 0x40000000 0x0 0x40000000>,
    > >>>>> <0x0 0xc0000000 0x3 0x0 0x0 0x40000000>,
    > >>>>> <0x1 0x0 0x0 0x80000000 0x0 0x40000000>,
    > >>>>> <0x1 0x40000000 0x0 0xc0000000 0x0 0x40000000>;
    > >>>>>
    > >>>>> not working for you? I haven't tried this myself, but since DT permits
    > >>>>> describing the inbound mappings this way, we should fix the code if it
    > >>>>> doesn't work at the moment.
    > >>>>
    > >>>> You mean encoding the memory controller index in the first cell? If that
    > >>>> works, that's indeed a much cleaner solution, though is it standard
    > >>>> compliant in any form?
    > >>>
    > >>> No those are just memory addresses (although I may have screwed up the
    > >>> order). From Documentation/devicetree/booting-without-of.txt:
    > >>>
    > >>> """
    > >>> Optional property:
    > >>> - dma-ranges: <prop-encoded-array> encoded as arbitrary number of triplets of
    > >>> (child-bus-address, parent-bus-address, length). Each triplet specified
    > >>> describes a contiguous DMA address range.
    > >>> """
    > >>>
    > >>
    > >> Then I am confused by your comment, that's what this patch does, it adds
    > >> support for reading "dma-ranges" from Device Tree and setting up inbound
    > >> windows using that. The only caveat is that because the PCIe root
    > >> complex has some ties with the memory bus architecture it is connected
    > >> to (SCB in our case) there is still a requirement to know the
    > >> translation between a given physical address and its backing memory
    > >> controller/aperture.
    > >>
    > >
    > > Ah ok, apologies for the noise then.
    > >
    > > I was hoping that having working support for dma-ranges would remove
    > > the need for the special phys<->dma conversion routines.
    >
    > What you describe definitively works with platform devices, but I am not
    > sure this is working for PCIe devices, although, conceptually it should,
    > yes.
    Sorry for my delay in responding. One problem is that
    of_dma_configure() only looks at the first dma-range given and then
    converts it to dev->dma_pfn_offset which is respected by the DMA API.
    However, we often have multiple dma-ranges, not just one. This is the
    big issue.

    There is another issue with of_dma_configure() being invoked by the EP
    driver on "bridge->parent->of_node", which is our RC device,
    Of_dma_configure() calls of_dma_range() on the of_get_next_parent() of
    our RC's device node and this misses the dma-ranges property which is
    contained within the RC. I think I could workaround this but there is
    no getting around the first problem.

    Thanks,
    Jim

    > --
    > Florian

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