This is intentional. ESWIN won’t publish the DC8000 datasheet because they probably don’t have the permission from IP vendor to do so. Best case scenario is that you can contact them and sign some NDA to get that. There’re however some info scattered around. Starfive’s JH7110 SoC uses DC8200, and they have more supplementary materials in there datasheet (no DC8200 register maps or details for sure). You can refer to the Display (HDMI out) controllers section on gentoo’s wiki:
It actually has a link back to this very post 
Another thing to reference is the kind of abandoned upstream patch (v5) from starfive:
It’s much cleaner and readable compared to the current ESWIN vendor kernel code, but still not clean enough for upstream to accept. Keep in mind that the IP used in JH7110 are likely different in someway.