I am currently working on board bring-up for our custom design based on the i.MX6D.
I have tried the i.Mx6DQSDL DDR3 Script Aid  and got mixed results. It is needed to
select the ARM core speed. Does this mean I need to run the semi-automatic calibration
process for every ARM core speed I want to support? u-boot start with ~800 MHz but
later on the linux kernel could change the ARM core speed up to 1.2 GHz.