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SubjectRe: UDMA is NFG on Ultra33 (CMD646 in disguise)

Mark when will you listen? Let me try this once more.

CMD646U chipsets, without hardware hacks, cannot be safely used in
_any_ UDMA mode whatsoever.

Several months ago, while you were still the IDE maintainer, I sent
you a precise description of this hardware bug in an email when I
found it during my coding of the driver for sparc64/PCI. And I also
told you the exact hardware change which is necessary to fix this, and
therefore why UDMA could not be enabled in a 646U driver we want any
users to use.

Don't fight this, if UDMA0 works for you, it is by luck and you are
hitting the edge of the chips reliable configuration. I know, becuase
I stuck a logic analyzer on these chips until the CMD people would
cough up an errata sheet for me.

So I ask that you please don't encourage the current IDE maintainers
to even think about adding support for any UDMA mode on cmd646U
chipsets.

Later,
David S. Miller
davem@dm.cobaltmicro.com

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