[Intel-gfx] [RFC] drm/i915: Add a new modparam for customized ring multiplier

[Yaodong Li]

>>> You are thinking of plugging into intel_pstate to make it smarter for ia freq transitions?
> Yep. This seems a correct step to give some automatic support instead of parameter/hardcoded multiplier.
>
Does this mean we should use cpufreq/intel_pstate based approach instead 
of the current modparam solution for Gen9?

Some concerns and questions about intel_pstate approach:
a) Currently, we cannot get the accurate pstate/target freq value from 
cpufreq in intel_pstate active mode since
      these values won't be exported to cpufreq layer, so if we won't 
change intel_pstate code then we only can get
      the max cpu freq of a new policy.
b) intel_pstate policy is attached to each logic cpu, which means we 
will receive policy/freq transition notification
     for each logic cpu freq change. One question is how we are going to 
decide the freq of the ring? just use the max
     cpu freq reported?
c) With the intel_pstate approach we may still run into thermal 
throttling, in this case, can a certain cooling device
     be triggered to lower the cpu freq?

Thanks and Regards,
-Jackie