6.17-stable review patch. If anyone has any objections, please let me know.
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From: Fangzhi Zuo Jerry.Zuo@amd.com
[ Upstream commit 12cdfb61b32a7be581ec5932e0b6a482cb098204 ]
[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 Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +- .../drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c | 13 ++++++++++--- .../drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h | 2 +- 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 aca57cc815514..afe3a8279c3a9 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -7974,7 +7974,7 @@ 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 77a9d2c7d3185..5412bf046062c 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 @@ -822,13 +822,20 @@ 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 600d6e2210111..179f622492dbf 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 @@ -59,7 +59,7 @@ 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,