[PATCH v2 3/9] drm/amdgpu: read back register after written

[David (Ming Qiang) Wu]

The addition of register read-back in VCN v2.5 is intended to prevent
potential race conditions.

Signed-off-by: David (Ming Qiang) Wu <david....@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/vcn_v2_5.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/vcn_v2_5.c 
b/drivers/gpu/drm/amd/amdgpu/vcn_v2_5.c
index 3eec1b8feaee..58b527a6b795 100644
--- a/drivers/gpu/drm/amd/amdgpu/vcn_v2_5.c
+++ b/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);
-- 
2.49.0