drm/amdgpu/vcn2.5: read back register after written

The addition of register read-back in VCN v2.5 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>

drivers/gpu/drm/amd/amdgpu/vcn_v2_5.c

@@ -1158,6 +1158,11 @@ static int vcn_v2_5_start_dpg_mode(struct amdgpu_vcn_inst *vinst, bool indirect)
 	WREG32_P(SOC15_REG_OFFSET(VCN, inst_idx, mmUVD_POWER_STATUS),
 		0, ~UVD_POWER_STATUS__STALL_DPG_POWER_UP_MASK);
 
+	/* Keeping one read-back to ensure all register writes are done,
+	 * otherwise it may introduce race conditions.
+	 */
+	RREG32_SOC15(VCN, inst_idx, mmUVD_STATUS);
+
 	return 0;
 }
 
@@ -1343,6 +1348,11 @@ static int vcn_v2_5_start(struct amdgpu_vcn_inst *vinst)
 	WREG32_SOC15(VCN, i, mmUVD_RB_SIZE2, ring->ring_size / 4);
 	fw_shared->multi_queue.encode_lowlatency_queue_mode &= ~FW_QUEUE_RING_RESET;
 
+	/* Keeping one read-back to ensure all register writes are done,
+	 * otherwise it may introduce race conditions.
+	 */
+	RREG32_SOC15(VCN, i, mmUVD_STATUS);
+
 	return 0;
 }
 
@@ -1569,6 +1579,11 @@ static int vcn_v2_5_stop_dpg_mode(struct amdgpu_vcn_inst *vinst)
 	WREG32_P(SOC15_REG_OFFSET(VCN, inst_idx, mmUVD_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, mmUVD_STATUS);
+
 	return 0;
 }
 
@@ -1635,6 +1650,10 @@ static int vcn_v2_5_stop(struct amdgpu_vcn_inst *vinst)
 		 UVD_POWER_STATUS__UVD_POWER_STATUS_MASK,
 		 ~UVD_POWER_STATUS__UVD_POWER_STATUS_MASK);
 
+	/* Keeping one read-back to ensure all register writes are done,
+	 * otherwise it may introduce race conditions.
+	 */
+	RREG32_SOC15(VCN, i, mmUVD_STATUS);
 done:
 	if (adev->pm.dpm_enabled)
 		amdgpu_dpm_enable_vcn(adev, false, i);