drm/amdgpu/vcn4.0.5: read back register after written

The addition of register read-back in VCN v4.0.5 is intended to prevent
potential race conditions.

Reviewed-by: Ruijing Dong <ruijing.dong@amd.com>
Signed-off-by: David (Ming Qiang) Wu <David.Wu3@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: davidwuAMD

drivers/gpu/drm/amd/amdgpu/vcn_v4_0_5.c

@@ -1254,6 +1254,11 @@ static void vcn_v4_0_5_stop_dpg_mode(struct amdgpu_vcn_inst *vinst)
 	/* disable dynamic power gating mode */
 	WREG32_P(SOC15_REG_OFFSET(VCN, inst_idx, regUVD_POWER_STATUS), 0,
 		~UVD_POWER_STATUS__UVD_PG_MODE_MASK);
+
+	/* Keeping one read-back to ensure all register writes are done,
+	 * otherwise it may introduce race conditions.
+	 */
+	RREG32_SOC15(VCN, inst_idx, regUVD_STATUS);
 }
 
 /**
@@ -1337,6 +1342,11 @@ static int vcn_v4_0_5_stop(struct amdgpu_vcn_inst *vinst)
 	/* enable VCN power gating */
 	vcn_v4_0_5_enable_static_power_gating(vinst);
 
+	/* Keeping one read-back to ensure all register writes are done,
+	 * otherwise it may introduce race conditions.
+	 */
+	RREG32_SOC15(VCN, i, regUVD_STATUS);
+
 done:
 	if (adev->pm.dpm_enabled)
 		amdgpu_dpm_enable_vcn(adev, false, i);