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    SubjectRe: [linux-usb-devel] pegasus + MediaGX: Oops in khubd, the continuing story?
    Date
    From
    > The Oops'es are mostly in the khubd process, but they sometimes appear in other
    > programs (insmod, ifconfig). They always lead to an immedate panic, and nothing

    I suspect the ohci driver currently. I've been reviewing it a little and it
    is full of code written by someone who does not know about pci write posting.

    Specifically

    writel(value, pciaddr)

    is a queued operation. So

    writel(value, foo)
    delay
    real(foo)

    might not do the writel into the delay is over or during it. PCI makes
    guarantees that

    - writes will go out in order and will be merged only if prefetchable set
    - multiple writes to the same addr will remain multiple writes
    - reads will not complete until the writes do

    This applies in both directions - bus mastering nasties abound notably


    writel(STOP, reg->dmactrl)
    kfree(buffer)

    is dangerous

    You have to do

    writel(STOP, reg->dmactrl);
    [posted]
    readl(reg->dmactrl)
    [read forces write, read reply will follow any DMA
    pending the other way]

    I've not attempted to fix it yet


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