github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-05-30 18:13:41 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

drm/amd/display: Fix pbn_div Calculation Error

Browse Source 
[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>
This commit is contained in:
Fangzhi Zuo 2025-04-08 15:11:43 -04:00 committed by Alex Deucher
parent 1bde5584e2
commit 12cdfb61b3
3 changed files with 12 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
View File

@ -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;

13
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
View File

@ -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 {

2
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h
View File

@ -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,