Subject: Re: [PATCH] Workaround for 745x data corruption bug

From: Benjamin Herrenschmidt <[email-masked]>
Date: Wed, 04 Aug 2004 10:45:32 +1000

> Looking at this errata, I don't think poeple using Marvell chips will
> be affected by this errata.
> I don't see this as impacting the IO subsystem only the internal MPX system. IE
> using a 2 74xx system and not using the M bit. This race can also
> occur on a single processor system with the M disabled, as it is in
> Linux, but it has nothing to do with the memory controller mapping its
> PCI<->mem windows as non cacheable. You should be able to boost the IO
> throughput using non coherency without this errata impacting you any
> more than it already is.
>
> Anyone please correct me if I am wrong because I need to know.

Note that I feel obligated to re-state again that doing non-coherent
DMA on a 6xx/7xx/7xxx CPU is a big no brainer and is asking for all sorts
of cache aliasing issues because of the way the kernel linear mapping of
memory is BAT mapped... (Note that 2.6 should be able to deal with the
DBAT beeing disabled, at the expense of perfs, though I'm pretty sure we
need the IBAT still set).

Ben.

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