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SubjectRe: [PATCH v5 04/12] PCI: brcmstb: add dma-range mapping for inbound traffic
On 20 September 2018 at 13:55, Florian Fainelli <> wrote:
> On 09/19/2018 07:19 PM, Ard Biesheuvel wrote:
>> On 19 September 2018 at 07:31, Jim Quinlan <> 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.

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