Re: UltraDMA on IBM Thinkpad

[Ted U <grendel@heorot.stanford.edu>]

On Mon, 17 Jun 2002 ira@crosswinds.net wrote:

> The fact is that OpenBSD downgrade to Pio Mode and so my CPU is always working for disk accesses.

> pciide0 at pci0 dev 15 function 0 "Acer Labs M5229 UDMA IDE" rev 0x20: DMA, channel 0 configured to compatibility, channel 1 configured to compatibility
> atapiscsi0 at pciide0 channel 1 drive 0
> scsibus0 at atapiscsi0: 2 targets
> atapiscsi0(pciide0:1:0): using PIO mode 3
> cd0 at scsibus0 targ 0 lun 0: <TOSHIBA, DVD-ROM SD-C2202, 1433> SCSI0 5/cdrom removable
> cd0(pciide0:1:0): using PIO mode 3

The Acer M5229 pciide driver disables DMA for ATAPI devices.  If you
really want to use DMA, edit the sys/dev/pci/pciide.c file.  Around line
3203 you can comment out the NO_DMA option being set.  Recompile, and
reboot.

Presumably there is a reason why DMA is disabled, though it seems other
operating systems use DMA.  I have a laptop that I "fixed" as above, and
it made a big difference in DVD performance.  If your system stops
working, go back to a normal kernel.



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