ata_piix and ide_generic weird behavior

[Alexandru Cabuz <alexcabuz@wanadoo.fr>]

Hello,

I have spent about the last week setting up the Debian AMD64 Sid port on my 
brand new AMD64 nforce3 box. 

I was wondering if anybody can explain the following behavior.

I have two ide DVD drives, one a regular ROM, the other RW. Since the 
ide_generic module does not support DMA, I learned that I needed the ata_piix 
module. That's great, but when I put both of them in my /etc/modules file, in 
any order, reboot, and then try to run 
hdparm -d1 /dev/hda
for example, it refuses, says 
/dev/hda:
 setting using_dma to 1 (on)
 HDIO_SET_DMA failed: Operation not permitted
 using_dma    =  0 (off)

The way to get it to work is to put only ata_piix in the /etc/modules file, 
and then, after it boot, you log in, and then do
modprobe ide_generic

And then, hdparm works and everything is cool.

But what is the difference between putting a module in /etc/modules and 
loading it with modprobe after boot?

Is it safe to load ide_generic only after boot, like in the /etc/profiles 
file?

I am using the 2.6.9-9 Debian kernel image.

Alex.