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    SubjectRe: ehci-hcd on CARDBUS hangs when stopping card service

    On Sat, 25 May 2002, David Brownell wrote:
    > Seems to me it'd be worth mentioning this issue somewhere in the
    > documentation or source. One could get the impression that the
    > main issue for a CardBus-enabled PCI driver is to make sure that
    > the "new style" driver APIs -- with a DEVICE_TABLE etc -- are used.
    > (Maybe just a brief comment in <asm/io.h> ...)

    Documentation might be a good thing, indeed. I doubt <asm/io.h> is the
    right place for it, people tend to look at other drivers etc to pattern
    after (as clearly showed by how often a bug in one place is replicated in
    lots of other places ;)

    We've actually fixed a number of these things - there are drivers that
    notice removal on their own silently, and just turn it into a no-op.

    > I'm hardly averse to changing that loop (which normally does have an end :)
    > and I expected to need to at some point. It's interesting to me just how
    > long that has been there without causing problems. In this case the root
    > cause is that Cardbus "improper shutdown sequence" problem, so "no end"
    > is just a particularly nasty secondary failure mode.

    Most people don't unplug their devices while they are in use, and on
    cardbus the most common case ends up (I think) being the fact that the
    cardbus PCI static interrupt itself is shared with the device interrupt.
    So what happens is that when you remove the CardBus card, that causes the
    cardbus controller to send an interrupt (for removal), but since that
    interrupt is shared with the card driver, the card driver also sees the
    interrupt even if the card itself is otherwise idle.

    This meant that some tulip cards at least were _guaranteed_ to lock up
    some time ago, simply because their interrupt handler would loop forever
    on seeing the "more work" bit continually (all bits in the status register
    were set due to the removal and floating data lines).


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