[PATCH] drm/amdgpu: getting fan speed pwm for vega10 properly

[Yury Zhuravlev <stalkerg@xxxxxxxxx>]

Hello,

During the setup, the fan manager https://github.com/markusressel/fan2go I found that my Vega56 was not working correctly. This fan manager expects what read PWM value should be the same as you wrote before, but it's not the case. PWM value was volatile, and what is more critical, if I wrote 200, after reading I saw ~70-100, which is very confusing.
After that, I started reading the amdgpu driver, and how fan speed works, and I found what PWM value was calculated from RPM speed and not correct for my case (different BIOS or fan configuration?).
Because it looked wrong, I started looking into different implementations and found that Vega20 used mmCG_FDO_CTRL1 and mmCG_THERMAL_STATUS registers to calculate the PWM value.
I also checked how we set PWM for Vega10 and found the same registers. After that, I copy-pasted the function from Vega20 to Vega10, and it started working much better. It still has some fluctuation, but as I understand, this behavior is expected.

I have no in-depth information about amdgpu, and the original function may have been for some reason (maybe for some broken BIOS?), but I suppose somebody forgot to backport this code after prototype implementation.

It would be my first patch here. Sorry if I skipped some procedures, will be appreciated it if you help me.

Regards,

---
diff --git a/drivers/gpu/drm/amd/pm/powerplay/hwmgr/vega10_thermal.c b/drivers/gpu/drm/amd/pm/powerplay/hwmgr/vega10_thermal.c
index dad3e3741a4e..190af79f3236 100644
--- a/drivers/gpu/drm/amd/pm/powerplay/hwmgr/vega10_thermal.c
+++ b/drivers/gpu/drm/amd/pm/powerplay/hwmgr/vega10_thermal.c
@@ -67,22 +67,21 @@ int vega10_fan_ctrl_get_fan_speed_info(struct pp_hwmgr *hwmgr,
 int vega10_fan_ctrl_get_fan_speed_pwm(struct pp_hwmgr *hwmgr,
                uint32_t *speed)
 {
-       uint32_t current_rpm;
-       uint32_t percent = 0;
-
-       if (hwmgr->thermal_controller.fanInfo.bNoFan)
-               return 0;
+       struct amdgpu_device *adev = hwmgr->adev;
+       uint32_t duty100, duty;
+       uint64_t tmp64;
 
-       if (vega10_get_current_rpm(hwmgr, &current_rpm))
-               return -1;
+       duty100 = REG_GET_FIELD(RREG32_SOC15(THM, 0, mmCG_FDO_CTRL1),
+                               CG_FDO_CTRL1, FMAX_DUTY100);
+       duty = REG_GET_FIELD(RREG32_SOC15(THM, 0, mmCG_THERMAL_STATUS),
+                               CG_THERMAL_STATUS, FDO_PWM_DUTY);
 
-       if (hwmgr->thermal_controller.
-                       advanceFanControlParameters.usMaxFanRPM != 0)
-               percent = current_rpm * 255 /
-                       hwmgr->thermal_controller.
-                       advanceFanControlParameters.usMaxFanRPM;
+       if (!duty100)
+               return -EINVAL;
 
-       *speed = MIN(percent, 255);
+       tmp64 = (uint64_t)duty * 255;
+       do_div(tmp64, duty100);
+       *speed = MIN((uint32_t)tmp64, 255);
 
        return 0;
 }
--