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    SubjectRe: [PATCH 2.6.22.y] ieee1394: revert "sbp2: enforce 32bit DMA mapping"
    Benjamin Herrenschmidt wrote:
    > Oh and, don't do the set_dma_mask() in sbp2, it has nothing to do there.
    > It should be in the ohci1394 driver.

    That's not quite right. OHCI-1394 implementations can go beyond 4GB bus
    address space. (Although I don't know if there are such implementations
    available. At least there are two implementations which can set the
    so-called Physical Range bigger than 4GB.)

    Sbp2 however requires that everything which it DMA-maps resides in the
    Physical Range of the controller. This way the CPU is not involved in
    most of the data transfers. The OHCI-1394 controller acts as bus bridge
    between IEEE 1394 bus and local bus, with a 1:1 mapping of IEEE 1394 bus
    addresses to and from local bus addresses --- but not in the whole 48
    bits white IEEE 1394 bus address range, only in the
    implementation-dependent Physical Range. The minimum Physical Range
    that all OHCI-1394 implementations guarantee is 4GB. I could actually
    have set a bigger mask in sbp2 when the controller supports a
    programmable bigger range.

    So that's the story why that dma_set_mask went into sbp2: Sbp2 wants
    mappings in a _subset_ of the OHCI-1394 controllers DMA range.

    Anyway. For now I will simply go with what 2.6.23-rc has and what
    2.6.21 had: No dma_set_mask anywhere in the 1394 subsystem. We can
    revisit this whenever an actual need arises.
    --
    Stefan Richter
    -=====-=-=== =--- --==-
    http://arcgraph.de/sr/
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