DMA Speed Select Problem (a bug ?)

[Ingo Rohloff]

Hi,

First of all I'm using linux-2.4.2.
After various reboots and frustration I finally found
out, why my machine did hang, as soon as I tried to burn
a CD on my ATAPI CD Burner.

Now I know why:
A look at /proc/ide/hdc relveals that
init_speed = 66

Which is wrong, because my CDBurner is only capable of
Multiword2 DMA transfers (speed 34).
Calling "hdparm -d1 -X34 /dev/hdc" fixes the problem.

I even found these messages in /var/log/messages:

Mar 14 18:01:48 pcrohloff kernel: hdc: set_drive_speed_status: status=0x51 {
DriveReady SeekComplete Error }
Mar 14 18:01:48 pcrohloff kernel: hdc: set_drive_speed_status: error=0x04

Which basically means that the linux driver even finds out that my
drive doesn't like UDMA66, but doesn't react to it.

I think that's a bug yes ?

I got a PIIX chipset, so this might be a problem of this specific
chipset driver  (piix.c). Then again probably not ...

so long
  Ingo Rohloff

PS: Burning a CD was only one trigger for the problem. In fact
    accessing my CDBurner in any way (like mounting a CD, or reading
    from it) will lock up my whole computer, as long as 
    "hdparm -d1 -X34" isn't called.
    It also doesn't depend on "ide-scsi" or "ide-cd" it will lock
    up with both modules.

    Also after unloading "ide-cd" and then reloading it, it is
    necessary to call "hdparm" again, because ide-cd will initialize
    the drive again with init_speed=66...