FC3: DVD DMA support vs libata, a (S)ATA(PI) nightmare?

[wwp]

Hello all!


I'm unsuccessfully struggling w/ DMA support for my Dell D810's DVD drive
(`hdparm -d 1 /dev/hdc` fails, and I get poor performances when
reading/writing, it even slows down the reactivity of the system).

I'm running out of ideas and even of hope, since none of my attempts to get
DMA were successful, and reading/writing CD/DVD w/ such prehistoric perfs :-).

I tried to customize/rebuild a 2.6.12-1.1381_FC3 kernel to get the following
lines in include/linux/libata.h:
  #define ATA_ENABLE_ATAPI
  #define ATA_ENABLE_PATA
then tried hdc=ide-scsi or hdc=scsi as boot params, loading ide-scsi module
thru /etc/rc.local, but nothing works. According to the variety of tests I
did, I get or not /dev/hdc, /dev/scd0 or /dev/sr0 (if I add the device node
manually), w/ various hdparm reports (read-ahead info present or not) but
hdparm always fails to set DMA:

/dev/(hdc|sr0|scd0):
 setting using_dma to 1 (on)
 HDIO_SET_DMA failed: Invalid argument

FYI, w/ default boot params of FC3 kernel, I get:
/dev/sda <- the hdd
/dev/hdc <- the CD/DVD drive (CD recorder)

If I use hdc=ide-scsi, /var/log/messages tells me:
  kernel: sr0: scsi3-mmc drive: 8x/24x writer cd/rw xa/form2 cdda tray
but I'm not that confident that ide-scsi should be used
since /var/log/messages tells me:
  ide-scsi is deprecated for cd burning! Use ide-cd and give dev=/dev/hdX as device

Any hint would be welcome, I'm definitely lost now! :-) Can't FC3 kernels
(even if modified) enable DMA for such DVD drives? Should I use a vanilla
kernel? How to use ide-cd? Is there life on Mars, and hope for me?

BTW: noticed that `modprobe -r ide-scsi` simply crashes the kernel, huhu.


References:
http://cri.ch/linux/docs/sk0010.html
http://www.lazy8.nu/delld180/DebianLinuxOnDellLattitude810laptop.html
http://casa.colorado.edu/~ajsh/alienware/index.html#DVD
http://tkrat.org/d810/
http://fedora.redhat.com/docs/release-notes/fc3/x86/


Regards,

-- 
wwp