Re: HPT372 DMA corruption

[Chuck Berg]

On Fri, Jan 09, 2004 at 03:24:28PM -0500, Richard B. Johnson wrote:
[cmp -l bad good]
> >  89260029   0  31
> >  89260030   0 327
> >  89260031   0 200
> >  89260032   0  13
> 
> Since whole bytes are not written, this looks strangely like
> an attempt to DMA to cached RAM! Since the CPU didn't write

I tested this by reading with O_DIRECT, and immediately after each read(),
read all of a 1MB array (my cache is only 256kB), and then checking the
data. The same corruption occurs. 

Via had a DMA corruption bug a couple years ago with similar symptoms,
apparently with the VT82C686B southbridge. Mine is a VT82C586B (which some
people also reported problems with). My board dates long after these
problems were discovered, so I sure hope it's not the same bug. I'll try
upgrading my BIOS to the latest version in case Soyo's changelog is not
entirely honest.

I did learn some more about the pattern of corruption. The data is not
being written to memory - the "bad" data is whatever happened to be there
before. It usually happens in 4, but sometimes 64 or 32 byte chunks.

When I read from the device with O_DIRECT, the corruption only appears at the
very end of the read. I've confirmed this for reads of 512 bytes through 256k
at multiples of 512 bytes.

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