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    SubjectRe: [PATCH 2/2] cciss: disable dma prefetch for P600
    On Wed, Oct 18, 2006 at 02:37:23PM -0700, Andrew Morton wrote:
    >
    > argh, you removed the mailing list from cc.

    Sorry, I'm still lacking proper etiquette.

    >
    > On Wed, 18 Oct 2006 11:54:53 -0500
    > "Mike Miller (OS Dev)" <mikem@beardog.cca.cpqcorp.net> wrote:
    >
    > > On Tue, Oct 17, 2006 at 05:10:21PM -0700, Andrew Morton wrote:
    > > > On Tue, 17 Oct 2006 16:13:03 -0500
    > > > "Mike Miller (OS Dev)" <mikem@beardog.cca.cpqcorp.net> wrote:
    > > >
    > > > > PATCH 2/2
    > > > > Turned off DMA prefetch for the P600 on systems which may present
    > > > > discontiguous memory.
    > > > >
    > > >
    > > > What do you mean by "discontiguous memory"? CONFIG_DISCONTIGMEM?
    > >
    > > The IPF memory map can have holes between the different regions. I've
    > > been told by our HW guys that AMD may also have holes.
    >
    > Pretty much all platforms/architectures have holes in their physical memory
    > map.
    >
    >
    > > >
    > > > What is the actual problem which is being fixed here?
    > >
    > > Sorry, I should have been clearer. There is a bug in the DMA engine that
    > > that may result in prefetching data from beyond the end of memory or
    > > falling off into one the holes on IPF and AMD. It causes a machine check
    > > when that happens.
    > > It doesn't happen on Proliant because the last 4kB (or so) of memory is
    > > mapped out by the BIOS and Pentium guarantees contiguous memory.
    >
    > I think that this:
    >
    > > > #if defined(CONFIG_IA64) || defined(CONFIG_X86_64)
    >
    > is nowhere near strong enough and is probably inappropriate.
    >
    > It _could_ be that CONFIG_DISCONTIGMEM|CONFIG_SPARSEMEM will be closer, but
    > even CONFIG_FLATMEM systems can have holes.

    I'm poking around on some IPF platforms. It looks like CONFIG_DISCONTIGMEM is
    set on them, but not the others you mention. Would that be sufficient?

    >
    > On what machines can/does this card exist? Things like powerpc?

    This problem was found on Itanium. We don't try to support powerpc.

    Thanks,
    mikem
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