Re: Crippling the IDE in 2.1.111 - IDE DMA or all DMA ?

Alan Cox (
Sat, 25 Jul 1998 22:55:26 +0100 (BST)

> Does that make DMA bad for disk IOs ? ;)

No. You misunderstand my interest. Im not interested in whether DMA, polled
I/O, or FIQ is the right way to do disk I/O. Im trying to find a pattern
to the reports of people who get disk corruption in 2.1.10x and dont in
2.0.x (I've eliminated several reports that also had 2.0.x problems already
and one person found the DMA problem was a CPU fan ;))

Im entirely interested in the following if people would like to mail me
reports (off list and I'll summarise)

Mail me only if they see disk corruption problems. The same procedure under
2.0.x doesnt cause problems (btw please for IDE test 2.0.34/35 with UDMA
support too).

o Disk controller type (IDE/SCSI) :
o Disk Hardware :
o Other devices on cable/chain :
o Does 2.0.33 also corrupt :
o Does 2.0.34/35 corrupt :
o Are you using RAID (md driver software) :
o What processor :
o What chipset :

> We must be aware that buses that donnot implement either parity or
> CRC may lead to _silent_ data corruption.

SCSI has parity and IDE has CRC. The IDE CRC was even done right - to a non
aware host the IDE CRC error appears to be a soft drive error. Only a UDMA
host realises its actually a cable CRC - so it fails safe


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