drm/amdgpu: Implement doorbell self-ring for NBIO 7.4

Fixes doorbell reflection on Vega20.

Change-Id: I0495139d160a9032dff5977289b1eec11c16f781
Signed-off-by: Jay Cornwall <Jay.Cornwall@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/nbio_v7_4.c

@@ -93,7 +93,20 @@ static void nbio_v7_4_enable_doorbell_aperture(struct amdgpu_device *adev,
 static void nbio_v7_4_enable_doorbell_selfring_aperture(struct amdgpu_device *adev,
 							bool enable)
 {
+	u32 tmp = 0;
 
+	if (enable) {
+		tmp = REG_SET_FIELD(tmp, DOORBELL_SELFRING_GPA_APER_CNTL, DOORBELL_SELFRING_GPA_APER_EN, 1) |
+		      REG_SET_FIELD(tmp, DOORBELL_SELFRING_GPA_APER_CNTL, DOORBELL_SELFRING_GPA_APER_MODE, 1) |
+		      REG_SET_FIELD(tmp, DOORBELL_SELFRING_GPA_APER_CNTL, DOORBELL_SELFRING_GPA_APER_SIZE, 0);
+
+		WREG32_SOC15(NBIO, 0, mmDOORBELL_SELFRING_GPA_APER_BASE_LOW,
+			     lower_32_bits(adev->doorbell.base));
+		WREG32_SOC15(NBIO, 0, mmDOORBELL_SELFRING_GPA_APER_BASE_HIGH,
+			     upper_32_bits(adev->doorbell.base));
+	}
+
+	WREG32_SOC15(NBIO, 0, mmDOORBELL_SELFRING_GPA_APER_CNTL, tmp);
 }
 
 static void nbio_v7_4_ih_doorbell_range(struct amdgpu_device *adev,