V3: patch for VCN v4.0.0 only Similar to the previous changes made for VCN v4.0.5, the addition of register read-back support in VCN v4.0.0 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 <[email protected]> Reviewed-by: Mario Limonciello <[email protected]> --- drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c | 4 ++++ 1 file changed, 4 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..070a2a8cdf6f 100644 --- a/drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c +++ b/drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c @@ -1122,6 +1122,10 @@ 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, regVCN_RB1_DB_CTRL); + return 0; } -- 2.34.1
