The ADP1653 data sheet shows two different modes for flash timing -- one of them is a set of 16 timeout values, ranging from 54.6 msec to 820 msec in multiples of 54.6 msec. The other is to keep the flash lit for as long as a particular input is held high, up to a maximum of 820 msec. As the supported V4L2 timing values go from "0-500" (and appear to be millisecond values), I was guessing that the second mechanism was in use, not the first...

In any case, I'll try to reconfigure the strobe controls to be a bit more cautious. Setting up the pause in terms of a duty cycle, rather than a raw timing value, sounds like a good idea for one thing.