drm/amdgpu/vcn3: read back register after written

[ Upstream commit b7a4842 ]

The addition of register read-back in VCN v3.0 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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/gpu/drm/amd/amdgpu/vcn_v3_0.c

@@ -1173,6 +1173,11 @@ static int vcn_v3_0_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;
 }
 
@@ -1360,6 +1365,11 @@ static int vcn_v3_0_start(struct amdgpu_vcn_inst *vinst)
 		fw_shared->multi_queue.encode_lowlatency_queue_mode &= cpu_to_le32(~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;
 }
 
@@ -1602,6 +1612,11 @@ static int vcn_v3_0_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;
 }
 
@@ -1674,6 +1689,11 @@ static int vcn_v3_0_stop(struct amdgpu_vcn_inst *vinst)
 	/* enable VCN power gating */
 	vcn_v3_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, mmUVD_STATUS);
+
 done:
 	if (adev->pm.dpm_enabled)
 		amdgpu_dpm_enable_vcn(adev, false, i);