IDE: PDC20275 turning on/off DMA dangerous?

[Clemens Koller <clemens.koller@anagramm.de>]

Hello!

I am working on an embedded ppc (mpc8540) using a pretty common Promise IDE
PCI controller w/ a PDC20275 on it (it's called Ultra TX2).
I have an otherwise good Maxtor 6B120P0 (160GB) connected to it.

But sometimes (expecially with more than zero disk-i/o-load), when I
turn on DMA by

$hdparm -X69 -d1 /dev/hda
I get 

hda: task_out_intr: status=0x58 { DriveReady SeekComplete DataRequest }
ide: failed opcode was: unknown
hda: CHECK for good STATUS

And when I turn off DMA with 
$hdparm -d0 /dev/hda
I get sometimes a

hda: DMA disabled

which is fine but sometimes I also get:

hda: status error: status=0x58 { DriveReady SeekComplete DataRequest }
ide: failed opcode was: unknown
hda: drive not ready for command
hda: CHECK for good STATUS

which is not so nice.
Can you tell me if this is dangerous?

$ uname -a 
Linux ecam.anagramm.de 2.6.13-rc7 #5 Thu Aug 25 15:33:38 CEST 2005 ppc ppc ppc GNU/Linux

I am about to update to the latest 2.6.15-rc5.

Thanks,
-- 
Clemens Koller
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