From: LinCheng Ku Date: Wed, 3 Dec 2025 02:18:16 +0000 (+0800) Subject: drm/amd/display: Add USB-C DP Alt Mode lane limitation in DCN32 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cea573a8e1ed83840a2173d153dd68e172849d44;p=thirdparty%2Fkernel%2Flinux.git 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 Signed-off-by: LinCheng Ku Signed-off-by: Chenyu Chen Tested-by: Daniel Wheeler Signed-off-by: Alex Deucher --- 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 44a4e3c4efb9c..65d28cb07b046 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); + } }