drm/amd/pm: a quick fix for "divided by zero" error

Considering Arcturus is a dedicated ASIC for computing, it
will be more proper to drop the support for fan speed reading
and setting. That's on the TODO list.
Signed-off-by: Evan Quan <evan.quan@amd.com>
Reported-by: Rui Teng <rui.teng@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/swsmu/smu11/arcturus_ppt.c

@@ -1227,8 +1227,12 @@ static int arcturus_get_fan_speed_rpm(struct smu_context *smu,
 
 		tmp64 = (uint64_t)crystal_clock_freq * 60 * 10000;
 		tach_status = RREG32_SOC15(THM, 0, mmCG_TACH_STATUS_ARCT);
+		if (tach_status) {
 			do_div(tmp64, tach_status);
 			*speed = (uint32_t)tmp64;
+		} else {
+			*speed = 0;
+		}
 
 		break;
 	}
@@ -1303,12 +1307,14 @@ static int arcturus_get_fan_speed_pwm(struct smu_context *smu,
 				CG_FDO_CTRL1, FMAX_DUTY100);
 	duty = REG_GET_FIELD(RREG32_SOC15(THM, 0, mmCG_THERMAL_STATUS_ARCT),
 				CG_THERMAL_STATUS, FDO_PWM_DUTY);
-	if (!duty100)
-		return -EINVAL;
 
+	if (duty100) {
 		tmp64 = (uint64_t)duty * 255;
 		do_div(tmp64, duty100);
 		*speed = MIN((uint32_t)tmp64, 255);
+	} else {
+		*speed = 0;
+	}
 
 	return 0;
 }

drivers/gpu/drm/amd/pm/swsmu/smu11/smu_v11_0.c

@@ -1306,8 +1306,13 @@ int smu_v11_0_get_fan_speed_rpm(struct smu_context *smu,
 	tmp64 = (uint64_t)crystal_clock_freq * 60 * 10000;
 
 	tach_status = RREG32_SOC15(THM, 0, mmCG_TACH_STATUS);
+	if (tach_status) {
 		do_div(tmp64, tach_status);
 		*speed = (uint32_t)tmp64;
+	} else {
+		dev_warn_once(adev->dev, "Got zero output on CG_TACH_STATUS reading!\n");
+		*speed = 0;
+	}
 
 	return 0;
 }