Bug#555702: Info received (ATA drive root partition "does not exist")
Comparing config-2.6.31-1-686[ for the not functioning kernel] with config-2.6.30-2-686 [for the functioning kernel] shows that the same modules to drive my IDE atiixp are used rather than the ATA atiixp ones. So there is no difference here. My IDE drive device hdX should be there rather than sdX, but it is not. Since the corresponding libata driver for atiixp is not engaged, it is not seen by libata either. But the sata drive is seen as per the functioning kernel. I suspect the new 2.6.31 kernel cannot work well with the old IDE atiixp driver.