diff options
| author | Fangzhi Zuo <Jerry.Zuo@amd.com> | 2025-04-08 15:11:43 -0400 |
|---|---|---|
| committer | Alex Deucher <alexander.deucher@amd.com> | 2025-09-05 17:38:41 -0400 |
| commit | 12cdfb61b32a7be581ec5932e0b6a482cb098204 (patch) | |
| tree | 5a456db78c71889dd22a1ecbca6b0f00341bdeed /drivers/gpu/drm/amd/display | |
| parent | 1bde5584e297921f45911ae874b0175dce5ed4b5 (diff) | |
drm/amd/display: Fix pbn_div Calculation Error
[Why]
dm_mst_get_pbn_divider() returns value integer coming from
the cast from fixed point, but the casted integer will then be used
in dfixed_const to be multiplied by 4096. The cast from fixed point to integer
causes the calculation error becomes bigger when multiplied by 4096.
That makes the calculated pbn_div value becomes smaller than
it should be, which leads to the req_slot number becomes bigger.
Such error is getting reflected in 8k30 timing,
where the correct and incorrect calculated req_slot 62.9 Vs 63.1.
That makes the wrong calculation failed to light up 8k30
after a dock under HBR3 x 4.
[How]
Restore the accuracy by keeping the fraction part
calculated for the left shift operation.
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Diffstat (limited to 'drivers/gpu/drm/amd/display')
3 files changed, 12 insertions, 5 deletions
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c index 5ae01b0ac093..e34d98a945f2 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -8015,7 +8015,7 @@ static int dm_encoder_helper_atomic_check(struct drm_encoder *encoder, if (IS_ERR(mst_state)) return PTR_ERR(mst_state); - mst_state->pbn_div.full = dfixed_const(dm_mst_get_pbn_divider(aconnector->mst_root->dc_link)); + mst_state->pbn_div.full = dm_mst_get_pbn_divider(aconnector->mst_root->dc_link); if (!state->duplicated) { int max_bpc = conn_state->max_requested_bpc; diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c index 6911c339bc61..5e92eaa67aa3 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c @@ -854,13 +854,20 @@ void amdgpu_dm_initialize_dp_connector(struct amdgpu_display_manager *dm, drm_connector_attach_dp_subconnector_property(&aconnector->base); } -int dm_mst_get_pbn_divider(struct dc_link *link) +uint32_t dm_mst_get_pbn_divider(struct dc_link *link) { + uint32_t pbn_div_x100; + uint64_t dividend, divisor; + if (!link) return 0; - return dc_link_bandwidth_kbps(link, - dc_link_get_link_cap(link)) / (8 * 1000 * 54); + dividend = (uint64_t)dc_link_bandwidth_kbps(link, dc_link_get_link_cap(link)) * 100; + divisor = 8 * 1000 * 54; + + pbn_div_x100 = div64_u64(dividend, divisor); + + return dfixed_const(pbn_div_x100) / 100; } struct dsc_mst_fairness_params { diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h index 65f76a7d00db..6f7ea684b555 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h @@ -60,7 +60,7 @@ enum mst_msg_ready_type { struct amdgpu_display_manager; struct amdgpu_dm_connector; -int dm_mst_get_pbn_divider(struct dc_link *link); +uint32_t dm_mst_get_pbn_divider(struct dc_link *link); void amdgpu_dm_initialize_dp_connector(struct amdgpu_display_manager *dm, struct amdgpu_dm_connector *aconnector, |