drm/amd/display: Add USB-C DP Alt Mode lane limitation in DCN32

Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

kernel os linux

[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>

authored by

LinCheng Ku and committed by

Alex Deucher 6 months ago cea573a8 db2373ad

+12 -3

1 changed file

expand all

drivers

gpu

drm

amd

display

dio

dcn32

dcn32_dio_link_encoder.c

+12 -3

drivers/gpu/drm/amd/display/dc/dio/dcn32/dcn32_dio_link_encoder.c

··· 188 188 if (!query_dp_alt_from_dmub(enc, &cmd)) 189 189 return; 190 190 191 - if (cmd.query_dp_alt.data.is_usb && 192 - cmd.query_dp_alt.data.is_dp4 == 0) 193 - link_settings->lane_count = MIN(LANE_COUNT_TWO, link_settings->lane_count); 191 + /* 192 + * USB-C DisplayPort Alt Mode lane count limitation logic: 193 + * When USB and DP share the same USB-C connector, hardware must allocate 194 + * some lanes for USB data, limiting DP to maximum 2 lanes instead of 4. 195 + * This ensures USB functionality remains available while DP is active. 196 + */ 197 + if (cmd.query_dp_alt.data.is_dp_alt_disable == 0 && 198 + cmd.query_dp_alt.data.is_usb && 199 + cmd.query_dp_alt.data.is_dp4 == 0) { 200 + link_settings->lane_count = 201 + MIN(LANE_COUNT_TWO, link_settings->lane_count); 202 + } 194 203 } 195 204 196 205

Configure Feed

Configure Feed