SIS 5513/IBM Deskstar HDIO_SET_DMA Operation not permitted?

[Rob Landley]

2.2 allowed me to set DMA on an SIS 5513 using an IBM
Deskstar 40 gig IDE.  2.4 goes "Operation not
permitted" when I try it.

Why?

I hit it with ide0=ata66 in lilo, and it sped up from
3 megs/sec to 5 megs/second, but I used to get 12. 
hdparm /dev/hda still says I'm not using DMA.

I realise I'm doing dangerous stuff here to get the
performance back.  I'm just curious why it's not doing
it for me.  (Is there a known problem I should be
worried about?)

Let's see, ide0=dma,ata66...  right?  Should I be
really really worried about my data integrity if I do
this?  It never had a problem under 2.2...

Rob

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