Enabling DMA in Ubuntu

I've been trying to enable DMA in Ubuntu. According to the 'Unofficial Ubuntu Guide' (http://ubuntuguide.org/) I first have to issue: hdparm -d1 /dev/cdrom I'm assuming this enables DMA only for the current session. Unfortuneatly, I get an error. Here's what the screen output looks like:

root@ubuntu:/home/me # hdparm -d1 /dev/cdrom

/dev/cdrom:
setting using_dma to 1 (on)
HDIO_SET_DMA failed: Operation not permitted
using_dma = 0 (off)

Nonetheless, I also edited my /etc/hdparm.conf to read:

/dev/cdrom {
dma = on
}

Ubuntu was previously installed on a small IDE drive. I was able to enable DMA then without any problems. I'm wondering if I have to enable some sort of SCSI emulation to get this new install to work ? If so, I would like to know how. Perhaps /dev/cdrom=ide-scsi ? However, I wouldn't know which file to insert it into.

Thanks

Dell OptiPlex GX200, 128 MB RAM
SCSI: 20GB Quantum Atlas with an Adaptec 29160N SCSI card.
IDE: SONY DVD RW DW-D22A, LG CD RW GCE-8525B IDE (Secondary IDE Controller)

/sda Quantum 20GB HD
/hdc Sony DVD-RW (Secondary Master)
/hdd LG CD-RW (Secondary Slave)

Hi

Using the hdparm -d1 /dev/cdrom will only enable dma for the current session but this command can be added to startup scripts to make it turn on dma on startup. I remembered reading something like this before so I did a quick search and found out that you cannot change the DMA setting on a device that is currently mounted, so you can try doing it when your CD drive isn't mounted (if you haven't tried that already). I don't know if this affects hard drives as I haven't changed DMA on a mounted hard drive before.

Reference: http://www.linuxquestions.org/questi...+not+permitted

I also found out that it may be a problem with your kernel. If support for your motherboard chipset isn't compiled into the kernel then DMA won't be supported. This means that you may have to recompile the kernel to get it to work. For some reason this has a reputation for being difficult, but I have recompiled several kernels with no problems and found it to be relatively easy.

Reference: http://www.linuxquestions.org/questi...+not+permitted

HTH

Richard

Thanks Richarde. I just went here: https://wiki.ubuntu.com/DMA and added the lines :
'piix
ide-core'
above 'ide-cd' and it seems to be working. (/etc/modules) I don't understand why it worked previously, but thats computers for you.