Both kernels 2.4.21 and 2.5.74 leave the SATA drive in PIO mode after
boot. My system is Abit NF7-S with 2 IBM 100MHz parallel drives on
IDE0, and 1 Western Digital 150 serial on IDE2.
NOTE: My boot drive in this case is the serial drive, and the parallel
drives are auxiliaries.
The 2 parallel drives come up dma on, udma5 marked(hdparm /dev/hde and
hdparm -i /dev/hde). The serial drive of course is dma off, nothing
marked. There is no way to turn on DMA in the BIOS.
2.5.74 allows me to execute "hdparm -d1 -Xudma6 /dev/hde" while booting
from a bootmisc.sh script. If I try the same thing with 2.4.21 I get
all kinds of errors, timeouts, other stuff and the EXT3 journal finally
aborts and shutdown gives I/O errors. I found out by trial and error
that if I execute with 2.4.21:
1)hdparm -Xudma6 /dev/hde This AOK, udma6 is on(marked)
2)hdparm -d1 /dev/hde Some errors show up, dma is set, but
udma6 is turned off(no mark)
3)hdparm -Xudma6 /dev/hde udma6 back on(marked)
A hdparm -t /dev/hde verifies udma6 on and working.
Another point. When my boot drive is /dev/hda, a parallel drive and the
serial drive, /dev/hde is the auxiliary 2.4.21 allows me to "hdparm -d1
-Xudma6 /dev/hde" while booting from a bootmisc.sh script.