mlord (
Wed, 17 Dec 1997 21:57:26 -0500

Roy P. Turner wrote:
> 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.

The 32-bit IO and multcount work only for PIO, not DMA.
On some drives (?), multcount might even slow down DMA,
though there is no evidence to support this theory.
Neither of these buys anything when DMA is used.

The write-caching can be turned on ("hdparm -W1") to speed up writing,
but one must be careful to turn it off again at system shutdown,
to ensure the cache is flushed before reset or poweroff.

> 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.

Mmm.. not sure what the issue might be.
See if things are any different with 2.1.73, when it appears.

The Linux IDE guy