drm/amdgpu/vcn2: read back register after written

The addition of register read-back in VCN v2.0 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_0.c

@@ -978,6 +978,12 @@ static int vcn_v2_0_start_dpg_mode(struct amdgpu_vcn_inst *vinst, bool indirect)
 	/* Unstall DPG */
 	WREG32_P(SOC15_REG_OFFSET(UVD, 0, 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(UVD, 0, mmUVD_STATUS);
+
 	return 0;
 }
 
@@ -1152,6 +1158,11 @@ static int vcn_v2_0_start(struct amdgpu_vcn_inst *vinst)
 	WREG32_SOC15(UVD, 0, 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(UVD, 0, mmUVD_STATUS);
+
 	return 0;
 }
 
@@ -1183,6 +1194,11 @@ static int vcn_v2_0_stop_dpg_mode(struct amdgpu_vcn_inst *vinst)
 	WREG32_P(SOC15_REG_OFFSET(UVD, 0, 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(UVD, 0, mmUVD_STATUS);
+
 	return 0;
 }
 
@@ -1248,6 +1264,11 @@ static int vcn_v2_0_stop(struct amdgpu_vcn_inst *vinst)
 	vcn_v2_0_enable_clock_gating(vinst);
 	vcn_v2_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, 0, mmUVD_STATUS);
+
 power_off:
 	if (adev->pm.dpm_enabled)
 		amdgpu_dpm_enable_vcn(adev, false, 0);