[PATCH v1 5/8] drm/amdgpu: read back register after written

[David (Ming Qiang) Wu]

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

Signed-off-by: David (Ming Qiang) Wu <David.Wu3 at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c b/drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c
index 8fff470bce87..d3c5c30f35bb 100644
--- a/drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c
+++ b/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_RB_WPTR);
+
 	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_RB_WPTR);
+
 	return 0;
 }
 
-- 
2.49.0