[Freedreno] [PATCH 2/8] drm/msm/dpu: drop performance tuning modes

[Abhinav Kumar]

On 6/19/2023 5:08 PM, Dmitry Baryshkov wrote:
> DPU performance module contains code to change performance state
> calculations. In addition to normal (sum plane and CRTC requirements),
> it can work in 'minimal' or 'fixed' modes. Both modes are impractical,
> since they can easily end up with the display underruns. Userspace also
> should not depend on these modes availability, since they are tuned
> through debugfs, which might not be available.
> 
> Drop relevant code to simplify performance state calculations.
> 
> Suggested-by: Konrad Dybcio <konrad.dybcio at linaro.org>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
> ---

Sorry but NAK on this change for two reasons:

This mode is not for usermode to depend on but for debugging. I have 
personally used both the perf max and perf min modes for debug.

1) The purpose is that, if you do see an underrun, you can force the 
perf mode as it will select max clk and bw rate

So something like below:

localhost /sys/kernel/debug/dri/1/debug/core_perf # echo 2 > perf_mode
localhost /sys/kernel/debug/dri/1/debug/core_perf # echo 300000000 > 
fix_core_clk_rate

This will allow us to force the clk to a particular value to see at what 
point it starts underruning

Also you can even do

localhost /sys/kernel/debug/dri/1/debug/core_perf # echo 1 > perf_mode

This will automatically max out the clk and BW

With this, you can figure out if underrun is a performance related 
underrun or a misconfiguration. We used it even recently to debug the 
performance issue with pclk reduction

2) Sometimes, you even want to force an underrun to debug devcoredump OR 
the recovery code. Forcing the min clk mode by doing

localhost /sys/kernel/debug/dri/1/debug/core_perf # echo 19200000 > 
fix_core_clk_rate
localhost /sys/kernel/debug/dri/1/debug/core_perf # echo 2 > perf_mode

Is the easiest way to trigger the recovery handler.

Hence I am not at all convinced of dropping this.