Not a Linux kernel person but really want to identify and fix this oops.
Have a old PC now used as firewall/print server/wireless VPN server,
that works fine on Linux 2.4.19 but dies on the new ide stuff that
came out after 2.4.19 (e.g. 2.4.22).

Some progress here but don't know who I talk to next. Is it a sis5513
problem or a ide-iops problem ?. I edited drivers/ide/ide-iops.c but
this may be because drivers/ide/pci/sis5513.c isn't setting up the
hwif structures right for the CDROM on the sis5513.

Its in the setup for the CDROM that fails. Its not a faulty CDROM drive
as this is all replaced and works OK in Mandrake 9.0 (i.e OLDER kernels).

Within sis5513.c the config_chipset_for_pio() calls ide_config_drive_speed() and passes drive of hdc (I now this works as I added some printk's of drive->name to get the name) and speed of 12 (Actual pio value is 4).

Then where the oops occurs is exactly at the line in the ide_iops.c line 911,

hwif->ide_dma_host_off(drive);

If I work around this line with a kludge edit like....

if (speed >= XFER_DMA_0 ) { hwif->ide_dma_host_off(drive); }

then the problem then oops at around line 978-981 at the
hwif->ide_dma_off_quietly(drive) i.e. ....

else
{
hwif->ide_dma_off_quietly(drive);
}

If I comment out ALL those lines then the oops stops. I created a
new bzImage with my changes and with isofs and joliet file system
as built-in and copied this bzImage to vmlinuz on a floppy (which
was made from the cdrom.img) replacing the original vmlinuz and
I was able to then get into 2nd stage install and into the normal
graphical install display OK.

Thus the chipset is a SIS5513. Its old and uses PIO modes and
NO DMA for the CDROM (hdc (or hdd on some printouts).
According to the normal dmeg (kernel2.4.19-16mdk),

ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx
SIS5513: IDE controller on PCI bus 00 dev 09
SIS5513: chipset revision 9
SIS5513: not 100% native mode: will probe irqs later
SiS5513
SIS5513: simplex device: DMA disabled
ide0: SIS5513 Bus-Master DMA disabled (BIOS)
SIS5513: simplex device: DMA disabled
ide1: SIS5513 Bus-Master DMA disabled (BIOS)
hda: WDC AC26400B, ATA DISK drive
hdc: ATAPI CD-ROM MAX 52X, ATAPI CD/DVD-ROM drive
ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
ide1 at 0x170-0x177,0x376 on irq 15

Kernel 2.4.22 (and above) has lots of changes to ide and something
is wrong here. What I did to line 911 is probably a valid kludge but
commenting out lines 97-981 may have other side effects.

BTW: I created my linux-2.4.22-10mdkBOOT source from linux2.4.22
plus added the boot config from the RPMS.

Oops is as follows on the Mandrake created linux-2.4.22-10mdkBOOT kernel.

Unable to handle kernel NULL pointer dereference at virtual address 00000000
printing eip:
00000000
*pde = 00000000
Oops: 0000

CPU: 0
EIP: 0010:[<00000000>] Not tainted
EFLAGS: 00010286
eax: 0000000c ebx: c013c840 ecx: 80000944 edx: 00000004
esi: c013c840 edi: c013c654 ebp: 0000000f esp: c113bf28
ds: 0018 es: 0018 ss: 0018
Process swapper (pid: 1, stackpage=c113b000)
Stack: c01ee618 c013c840 00b400f0 00000001 0c102170 00000004 c013c840 00000001
0000000f c01ecc8d c013c840 0000000c 0413c654 c013c840 c013c654 c01fbddf
c013c840 000000ff 00000246 00000001 c013c654 c0248000 0004e000 c01fc6bb
Call Trace: [] [] [] [] []
[] []
Code: Bad EIP value.
<0>Kernel panic: Attmpting to kill init!