diff options
| author | LinCheng Ku <lincheng.ku@amd.com> | 2025-12-03 10:18:16 +0800 |
|---|---|---|
| committer | Alex Deucher <alexander.deucher@amd.com> | 2025-12-16 13:25:25 -0500 |
| commit | cea573a8e1ed83840a2173d153dd68e172849d44 (patch) | |
| tree | 4bed1f7439710295aec218565eac2a6806364af8 | |
| parent | db2373ad05d41069f3eb39c6963a131b7fdc9f2b (diff) | |
drm/amd/display: Add USB-C DP Alt Mode lane limitation in DCN32
[Why]
USB-C DisplayPort Alt Mode with concurrent USB data needs lane count
limitation to prevent incorrect 4-lane DP configuration when only 2 lanes
are available due to hardware lane sharing between DP and USB3.
[How]
Query DMUB for Alt Mode status (is_dp_alt_disable, is_usb, is_dp4) in
dcn32_link_encoder_get_max_link_cap() and cap DP to 2 lanes when USB is
active on USB-C port. Added inline documentation explaining the USB-C
lane sharing constraint.
Reviewed-by: PeiChen Huang <peichen.huang@amd.com>
Signed-off-by: LinCheng Ku <lincheng.ku@amd.com>
Signed-off-by: Chenyu Chen <chen-yu.chen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
| -rw-r--r-- | drivers/gpu/drm/amd/display/dc/dio/dcn32/dcn32_dio_link_encoder.c | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/drivers/gpu/drm/amd/display/dc/dio/dcn32/dcn32_dio_link_encoder.c b/drivers/gpu/drm/amd/display/dc/dio/dcn32/dcn32_dio_link_encoder.c index 44a4e3c4efb9..65d28cb07b04 100644 --- a/drivers/gpu/drm/amd/display/dc/dio/dcn32/dcn32_dio_link_encoder.c +++ b/drivers/gpu/drm/amd/display/dc/dio/dcn32/dcn32_dio_link_encoder.c @@ -188,9 +188,18 @@ void dcn32_link_encoder_get_max_link_cap(struct link_encoder *enc, if (!query_dp_alt_from_dmub(enc, &cmd)) return; - if (cmd.query_dp_alt.data.is_usb && - cmd.query_dp_alt.data.is_dp4 == 0) - link_settings->lane_count = MIN(LANE_COUNT_TWO, link_settings->lane_count); + /* + * USB-C DisplayPort Alt Mode lane count limitation logic: + * When USB and DP share the same USB-C connector, hardware must allocate + * some lanes for USB data, limiting DP to maximum 2 lanes instead of 4. + * This ensures USB functionality remains available while DP is active. + */ + if (cmd.query_dp_alt.data.is_dp_alt_disable == 0 && + cmd.query_dp_alt.data.is_usb && + cmd.query_dp_alt.data.is_dp4 == 0) { + link_settings->lane_count = + MIN(LANE_COUNT_TWO, link_settings->lane_count); + } } |