no cd/dvd devices detected after kernel change

[Joe Hickey <joseph@hickey.org.uk>]

Hello,

Using 2.6.24-1-686, my two IDE-connected cd/dvd drives are detected as
/dev/sr0 and /dev/sr1, symlinked to cdrom0 and cdrom1, and work
perfectly. When I boot 2.6.25-2-686-bigmem, no entries for these
devices appear in /dev.

With the working kernel, the relevant part of dmesg is:

scsi7 : SCSI emulation for USB Mass Storage devices
usb-storage: device found at 2
usb-storage: waiting for device to settle before scanning
ata5.00: ATAPI: HL-DT-STDVD-RAM GSA-H55L, 1.05, max UDMA/66
ata5.01: ATAPI: HL-DT-ST DVD-ROM GDR-H30N, 1.00, max UDMA/33
usb 7-2: new low speed USB device using uhci_hcd and address 2
ata5.00: configured for UDMA/66
usb 7-2: configuration #1 chosen from 1 choice
ata5.01: configured for UDMA/33
BAR5:00:02 01:7F 02:22 03:CA 04:00 05:00 06:00 07:00 08:00 09:00 0A:00
0B:00 0C:07 0D:00 0E:00 0F:00 

With the bigmem kernel, what looks like the corresponding part of
dmesg:

[    0.812202] PCI: Setting latency timer of device 0000:03:00.0 to 64
[    0.812281] scsi5 : ahci
[    0.812455] scsi6 : ahci
[    0.812583] scsi7 : ahci
[    0.812645] ata5: SATA max UDMA/133 abar m1024@0xfeaffc00 port
0xfeaffd00 irq 16
[    0.812705] ata6: SATA max UDMA/133 abar m1024@0xfeaffc00 port
0xfeaffd80 irq 16
[    0.812765] ata7: DUMMY
[    0.874732] usb 7-1: configuration #1 chosen from 1 choice
[    0.875046] scsi8 : SCSI emulation for USB Mass Storage devices
[    0.875218] usb 7-1: New USB device found, idVendor=04b4,
idProduct=6830

There are no error messages referring to the DVD drives elsewhere in
dmesg.

There's a slight difference in the output of lsmod | grep ide between
the two kernels. For the working kernel:

ide_cd                 36224  0 
cdrom                  32512  2 ide_cd,sr_mod
ide_core              108292  2 ide_cd,generic

For the bigmem kernel that doesn't detect the drives:

ide_cd_mod             33632  0 
cdrom                  32640  2 sr_mod,ide_cd_mod
ide_pci_generic         4996  0 [permanent]
ide_core              101624  2 ide_cd_mod,ide_pci_generic

I have ide-core, ide-cd, cdrom and sr_mod listed in /etc/modules to
try to ensure relevant stuff gets loaded at boot.

I'd appreciate any advice about next steps for tracking down the
problem.

Best,
-- 
Joe Hickey