Roy P. Turner (ecstasy@dopamine.com)
Wed, 17 Dec 1997 20:31:34 -0600

First of all, is Ultra DMA fully supported in the linux 2.1 kernel?

I just added a WD AC12100 UDMA drive to one of my linux machines and it
seems to detect it as UDMA and yes, it is faster. Doing an hdparm on
the drive came back with the following.

multcount = 0 (off)
I/O support = 0 (default 16-bit)
unmaskirq = 1 (on)
using_dma = 1 (on)
keepsettings = 0 (off)
nowerr = 0 (off)
readonly = 0 (off)
readahead = 8 (on)
geometry = 4092/16/63, sectors = 4124736, start = 0

DMA is turned on already, but I want to tweak performance a little by
setting I/O to 32 bit, the multcount to 16, and enabling write cacheing.
This has worked fine on the 5 other non UDMA Western Digital drives I
use, but enabling these features on the new UDMA drive causes the drive
to continuously timeout and become unusable. I have to settle for the
default bootup settings in order to use the drive. I'm just curious if
this seems to be a kernel problem, hardware problem, or an hdparm problem.