I spoke too soon. It just flat out does not work to have sf100 and 256Mbit part AFAICT

On Fri, Sep 28, 2018 at 11:19 AM ron minnich <rminnich@gmail.com> wrote:
Got the fix. I used dpcmd to update the firmware on the FS100 to 5.5.3

Then flashrom can program it with ease.

And, ironically, while dpcmd can update the firmware, it still can't flash the part :-)