drm/amdgpu/vcn4: read back register after written

The addition of register read-back in VCN v4.0.0 is intended to prevent
potential race conditions.

Reviewed-by: Ruijing Dong <[email protected]>
Signed-off-by: David (Ming Qiang) Wu <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

Author: davidwuAMD

drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c

@@ -1122,6 +1122,11 @@ static int vcn_v4_0_start_dpg_mode(struct amdgpu_vcn_inst *vinst, bool indirect)
 			ring->doorbell_index << VCN_RB1_DB_CTRL__OFFSET__SHIFT |
 			VCN_RB1_DB_CTRL__EN_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);
+
 	return 0;
 }
 
@@ -1303,6 +1308,11 @@ static int vcn_v4_0_start(struct amdgpu_vcn_inst *vinst)
 	WREG32_SOC15(VCN, i, 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, i, regUVD_STATUS);
+
 	return 0;
 }
 
@@ -1583,6 +1593,11 @@ static void vcn_v4_0_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);
 }
 
 /**
@@ -1666,6 +1681,11 @@ static int vcn_v4_0_stop(struct amdgpu_vcn_inst *vinst)
 	/* enable VCN power gating */
 	vcn_v4_0_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);