[Bug 85021] radeon: Allow one to set "mid" to power_dpm_force_performance_level

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=85021

--- Comment #6 from Alex Deucher <alexdeucher at gmail.com> ---
(In reply to higuita from comment #2)
> Auto will jump from level 0 to level 2, i never see level 1 being used in
> any place/app other than a maximized glxgears.
> 
> tvtime or chrome+youtube+thml5 will jump the level from 0 to 2, but if i
> force low i see no problem at all, no drop frames, no lag. Only if i try to
> open more things at same time (many terminals doing dmesg, many videos
> playing, some 3d game) it starts to get slower. 
> so clearly the high is too much, low is enough for most use cases and mid
> would be perfect.  Auto will not put it in mid.
> 

It's all based on GPU load.  The hw steps through the performance levels based
on demand.

> That is why i wanted to manually setup the mid level, the computer keeps
> cool and the gpu power is good enough for almost all load (other than heavy
> 3D games)
> 
> also, its a little strange that low and high is supported in dpm setting,
> but not the mid... profile setting had the low, mid, high and the auto

The problem is twofold:

1. Most asics do not provide an easy way to lock the performance level to just
the mid state.

2. Only relatively old asics support a real mid performance level.  The last
few generations only support low and high limits and the hw changes through a
large number of dynamically generated states in between.

The only way to do that would be to dynamically generate a new state with mid
being the high state (e.g., low mid mid, or low mid, etc. depending on the
asic) and then switch to that state and lock it into the "high" performance
level of that state.  Unforunately, a full state change is a relatively heavy
operation compared to just locking the performane level of an already loaded
state.

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