DMA for DVD-Drive

[klausabc]

I want to activate DMA for my DVD-Writer.
The drive is secondary master. but
hdparm /dev/hdc
/dev/hdc:
HDIO_GET_MULTCOUNT failed: Invalid argument
IO_support = 1 (32-bit)
unmaskirq = 1 (on)
using_dma = 0 (off)
keepsettings = 0 (off)
readonly = 0 (off)
BLKRAGET failed: Invalid argument
HDIO_GETGEO failed: Invalid argument

hdparm -d1 /dev/hdc

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

I have read a few messages about this topic:
I have dma support in the kernel (because dma is active for hda)
the drive is not currently mounted
I am using ide-scsi (in lilo.conf i got a line append="hdc=scsi" )


suggestions are welcome

[klausabc]

my guess is, that ide-scsi is blocking the activation of DMA,
so I removed the kernel parameter hdc=scsi, but ide-scsi is
still used for hdc
I am using knoppix 3.4, kernelversion 2.4.26