drm/amdgpu/vcn5.0.1: read back register after written

The addition of register read-back in VCN v5.0.1 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_v5_0_1.c

@@ -1038,6 +1038,11 @@ static int vcn_v5_0_1_start(struct amdgpu_vcn_inst *vinst)
 	WREG32_SOC15(VCN, vcn_inst, regVCN_RB_ENABLE, tmp);
 	fw_shared->sq.queue_mode &= ~(FW_QUEUE_RING_RESET | FW_QUEUE_DPG_HOLD_OFF);
 
+	/* Keeping one read-back to ensure all register writes are done,
+	 * otherwise it may introduce race conditions.
+	 */
+	RREG32_SOC15(VCN, vcn_inst, regUVD_STATUS);
+
 	return 0;
 }
 
@@ -1072,6 +1077,11 @@ static void vcn_v5_0_1_stop_dpg_mode(struct amdgpu_vcn_inst *vinst)
 	/* disable dynamic power gating mode */
 	WREG32_P(SOC15_REG_OFFSET(VCN, vcn_inst, 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, vcn_inst, regUVD_STATUS);
 }
 
 /**
@@ -1147,6 +1157,11 @@ static int vcn_v5_0_1_stop(struct amdgpu_vcn_inst *vinst)
 	/* clear status */
 	WREG32_SOC15(VCN, vcn_inst, regUVD_STATUS, 0);
 
+	/* Keeping one read-back to ensure all register writes are done,
+	 * otherwise it may introduce race conditions.
+	 */
+	RREG32_SOC15(VCN, vcn_inst, regUVD_STATUS);
+
 	return 0;
 }