Re: HPT372 DMA corruption

[Måns Rullgård]

Chuck Berg <chuck@xxxxxxxxxx> writes:

> 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.

Well, VIA never did have a good reputation.

> 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.

Is it always a multiple of 4 bytes?  Is there any pattern in the
position of the corruption, such as always aligned to some value?

> 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.

Could something be cutting off the DMA transfer too early?

-- 
Måns Rullgård
mru@xxxxxx

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