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    SubjectRe: [PATCH 13/18] arm64: ioremap: use nGnRnE mappings on platforms that require it
    Date
    On 09/02/2021 18.15, Arnd Bergmann wrote:
    > Right, these are the same ranges that I found in the adt and that Mark
    > listed in his code snippet, so it seems we all see the same partitioning
    > of the address space. I also see them reflected in the
    > /defaults/pmap-io-ranges property in ADT, which seems to have an entry
    > for every register range that has some mmio registers, along with what
    > appears to be a bitmask of some attributes, and it clearly shows
    > the above ranges as having a distinct set of bits from the others
    > (in little-endian):
    >
    > 00000000 04000000 00000080 00000000 27000080 65494350
    > 00000080 04000000 00000080 00000000 27000080 65494350
    > 00000080 05000000 00000080 00000000 27000080 65494350
    > 00000000 06000000 00000080 00000000 27000080 65494350
    > 000000a0 06000000 00000020 00000000 27000080 65494350
    > 000000c0 06000000 00000040 00000000 27000080 65494350
    > ^64-bit address ^64-bit length ^ 64-bit flags?

    That's ASCII :-)

    'PCIe'

    >
    > As opposed to e.g.
    >
    > 0000f002 05000000 00400000 00000000 07400000 54524144

    'DART'

    > 00800021 05000000 00400000 00000000 07400000 44495344

    'DSID'

    > Ok, so if we want this to get encoded in a 'struct resource' flag, the PCI
    > resources should work just fine as these resources come from the
    > PCI layer rather than of_address_to_resource(). I think it would be
    > reasonable here to add something to of_address_to_resource() to
    > set such a flag if we can find an unused one, and then require the
    > drivers for this platform to go through devm_ioremap_resource()
    > or similar.

    This sounds reasonable. For setting such a flag, I guess looking for a
    property (inherited from parents) would make sense. `mmio-map-mode =
    "nonposted"` or something like that?

    --
    Hector Martin (marcan@marcan.st)
    Public Key: https://mrcn.st/pub

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