Hm, I patched the kernel with 2.6.11-libata-dev1, compiled it with

# CONFIG_BLK_DEV_PDC202XX_NEW is not set
CONFIG_BLK_DEV_VIA82CXXX=y   (for the motherboard IDE)
CONFIG_SCSI=y
CONFIG_SCSI_SATA=y
CONFIG_SCSI_PATA_PDC2027X=y

and rebooted. SCSI is initialized and the pata_pdc2027x driver is
loaded, but it doesn't seem to find any devices. Or maybe it doesn't
look for devices at all. I can tell that it's loaded by the existence
of /sys/bus/pci/drivers/pata_pdc2027x (a directory which is empty).

/proc/scsi/scsi is also empty besides the "Attached devices:" line.
During startup the kernel does say "Probing IDE interface ide0"
through "ide5" (finding only devices on ide0). I also tried compiling
pata_pdc2027x as a module, with same result.

What's wrong here?

I think I know what the problem is.

In include/linux/libata.h, make sure the preprocessor declarations are as 
follows.  I think the defaults have ATA_ENABLE_PATA undefined.

#define ATA_ENABLE_ATAPI        /* undefine to disable ATAPI support */
#define ATA_ENABLE_PATA          /* define to enable PATA support in some
                                 * low-level drivers */

Sorry I forgot to mention this earlier.  

Drew