[PATCH 2/2] drm/amdgpu: read back DB_CTRL register for VCN v4.0.0 and v5.0.0

[David (Ming Qiang) Wu]

Similar to the previous changes made for VCN v4.0.5, the addition of
register read-back support in VCN v4.0.0 and v5.0.0 is intended to
prevent potential race conditions, even though such issues have not
been observed yet. This change ensures consistency across different
VCN variants and helps avoid similar issues on newer or closely
related GPUs. The overhead introduced by this read-back is negligible.

Signed-off-by: David (Ming Qiang) Wu <David.Wu3 at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c   | 4 ++++
 drivers/gpu/drm/amd/amdgpu/vcn_v5_0_0.c | 4 ++++
 2 files changed, 8 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..24d4077254df 100644
--- a/drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c
@@ -1121,6 +1121,8 @@ static int vcn_v4_0_start_dpg_mode(struct amdgpu_vcn_inst *vinst, bool indirect)
 	WREG32_SOC15(VCN, inst_idx, regVCN_RB1_DB_CTRL,
 			ring->doorbell_index << VCN_RB1_DB_CTRL__OFFSET__SHIFT |
 			VCN_RB1_DB_CTRL__EN_MASK);
+	/* Read DB_CTRL to flush the write DB_CTRL command. */
+	RREG32_SOC15(VCN, inst_idx, regVCN_RB1_DB_CTRL);
 
 	return 0;
 }
@@ -1282,6 +1284,8 @@ static int vcn_v4_0_start(struct amdgpu_vcn_inst *vinst)
 	WREG32_SOC15(VCN, i, regVCN_RB1_DB_CTRL,
 		     ring->doorbell_index << VCN_RB1_DB_CTRL__OFFSET__SHIFT |
 		     VCN_RB1_DB_CTRL__EN_MASK);
+	/* Read DB_CTRL to flush the write DB_CTRL command. */
+	RREG32_SOC15(VCN, i, regVCN_RB1_DB_CTRL);
 
 	WREG32_SOC15(VCN, i, regUVD_RB_BASE_LO, ring->gpu_addr);
 	WREG32_SOC15(VCN, i, regUVD_RB_BASE_HI, upper_32_bits(ring->gpu_addr));
diff --git a/drivers/gpu/drm/amd/amdgpu/vcn_v5_0_0.c b/drivers/gpu/drm/amd/amdgpu/vcn_v5_0_0.c
index 27dcc6f37a73..d873128862e4 100644
--- a/drivers/gpu/drm/amd/amdgpu/vcn_v5_0_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/vcn_v5_0_0.c
@@ -793,6 +793,8 @@ static int vcn_v5_0_0_start_dpg_mode(struct amdgpu_vcn_inst *vinst,
 	WREG32_SOC15(VCN, inst_idx, regVCN_RB1_DB_CTRL,
 		ring->doorbell_index << VCN_RB1_DB_CTRL__OFFSET__SHIFT |
 		VCN_RB1_DB_CTRL__EN_MASK);
+	/* Read DB_CTRL to flush the write DB_CTRL command. */
+	RREG32_SOC15(VCN, inst_idx, regVCN_RB1_DB_CTRL);
 
 	return 0;
 }
@@ -925,6 +927,8 @@ static int vcn_v5_0_0_start(struct amdgpu_vcn_inst *vinst)
 	WREG32_SOC15(VCN, i, regVCN_RB1_DB_CTRL,
 		     ring->doorbell_index << VCN_RB1_DB_CTRL__OFFSET__SHIFT |
 		     VCN_RB1_DB_CTRL__EN_MASK);
+	/* Read DB_CTRL to flush the write DB_CTRL command. */
+	RREG32_SOC15(VCN, i, regVCN_RB1_DB_CTRL);
 
 	WREG32_SOC15(VCN, i, regUVD_RB_BASE_LO, ring->gpu_addr);
 	WREG32_SOC15(VCN, i, regUVD_RB_BASE_HI, upper_32_bits(ring->gpu_addr));
-- 
2.49.0