ADC differences between -bone68 and -bone72?

I'm having issues with ADC in 3.8.13 (device or resource busy errors). Googling, the answer is always that the ADC is in continuous mode, and to disable that using the "mode" node in sysfs.

But I have no "mode" node.

On a different BBB running 3.8.13-bone68 (wheezy 7.7), I have no "mode" node, and ADC works fine. On this BBB with 3.8.13-bone72 (wheezy 7.8), I get the errors.

I just tried copying the -bone68 kernel and associated files to my -bone72 board, and ADC seems to work properly.

Looking at the ti_am335x_adc.c code between the two revisions, and they're identical. Not sure what else is getting in the way.