DMA disabled on IDE controller, VIA KT600 chipset

[Neilen Marais]

Hi!

I ran debian with a stock 2.6.10 (I know, I'm crazy) kernel, and had no
problem using DMA with my IDE optical drives and HDD. Now that I'm using
ubuntu, neither is DMA enabled by default, nor can I use hdparm to fix
it! I get:

root at wanbalans:/home/brick # hdparm -d1 /dev/hdd

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

Luckily, I decided to buy a new SATA drive to install ubuntu on even
before I knew of this problem. The SATA drive works great. It gets
50MB/s+ with low CPU usage (damn, that's faster than my 486 could read
from buffercache.) 

However, if I copy something from my old drive, performance is horrible,
with 100% CPU and choppy interface. Writing CDs is even worse. If I
write anything faster than 16x, I get tons of buffer underruns.

>From the hdparm output it seems like my IDE controller is on a kernel
blacklist or something. If this is so, I think it's a mistake, since it
was rock solid with DMA before.

Anyway, I'm using an el-cheapo (Chaintek I think?) board with a VIA
KT600 chipset and an Athlon XP. My hard drives are both Seagates, my
optical drives are branded as Asus and Benq. Some potentially useful
lspci output lines are:

0000:00:00.0 Host bridge: VIA Technologies, Inc. VT8377 [KT400/KT600 AGP] Host Bridge (rev 80)
0000:00:01.0 PCI bridge: VIA Technologies, Inc. VT8237 PCI Bridge
0000:00:0f.0 IDE interface: VIA Technologies, Inc. VIA VT6420 SATA RAID Controller (rev 80)
0000:00:0f.1 IDE interface: VIA Technologies, Inc. VT82C586A/B/VT82C686/A/B/VT823x/A/C PIPC Bus Master IDE (rev 06)

help appreciated!

Thanks
Neilen