As I said in my reply, I have been porting my phone which has a 665, an SoC released 2 years after the 845, and it's a pretty smooth process. Each SoC has a different topology and vendor quirks, but they use the same few drivers and interconnects (glink, rpm, smd, etc). Many of the drivers I am using are for components more recent than the 845, upstreamed by Linaro and Qcom folks.