Hi, On DCE8-class ASICs (e.g. Bonaire), the resource pool contains digital DIG stream encoders plus one analog DAC encoder. When assigning a stream encoder for a second DisplayPort MST stream, if the preferred digital encoder is already acquired, dce100_find_first_free_match_stream_enc_for_link() falls back to the first free pool entry. That entry may be the analog encoder, whose funcs table lacks DP hooks such as dp_set_stream_attribute. The subsequent atomic commit then dereferences NULL function pointers in link_set_dpms_on() and crashes.
Skip encoders without dp_set_stream_attribute when the stream uses a DP signal (including MST). Use dc_is_dp_signal(stream->signal) for the MST fallback path instead of checking only the link connector signal. Tested on: - GPU: AMD Radeon R7 260X (Bonaire / DCE8) - Board: Supermicro C9X299-PG300 - Setup: DP MST daisy chain, either hotplug second monitor or have it connected on boot - Kernel: 7.1.3 (issue observed since 6.19) - Result: kernel oops without patch; dual monitors stable with patch Thanks, Andriy Korud
From d77178fe6f2cbf54f6be8c1e3c49108849e53eba Mon Sep 17 00:00:00 2001 From: Andriy Korud <[email protected]> Date: Thu, 9 Jul 2026 19:27:34 +0200 Subject: [PATCH drm-amd] drm/amd/display: dce100: skip non-DP stream encoders for DP MST On DCE8-class ASICs (e.g. Bonaire), the resource pool contains digital DIG stream encoders plus one analog DAC encoder. When assigning an encoder for a second DisplayPort MST stream, if the preferred digital encoder is already acquired, dce100_find_first_free_match_stream_enc_for_link() falls back to the first free pool entry. That entry may be the analog encoder, whose funcs table lacks DP hooks (dp_set_stream_attribute, etc.). The subsequent atomic commit then dereferences NULL function pointers in link_set_dpms_on() and crashes. Skip encoders without dp_set_stream_attribute when the stream uses a DP signal (including MST). Use dc_is_dp_signal(stream->signal) for the MST fallback path instead of checking only the link connector signal. Reproduced on Radeon R7 260X (Bonaire) with DP MST hotplug of a second monitor on Linux 6.19+. Signed-off-by: Andriy Korud <[email protected]> --- .../drm/amd/display/dc/resource/dce100/dce100_resource.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/amd/display/dc/resource/dce100/dce100_resource.c b/drivers/gpu/drm/amd/display/dc/resource/dce100/dce100_resource.c index b92d4f378d60..beaf2e654672 100644 --- a/drivers/gpu/drm/amd/display/dc/resource/dce100/dce100_resource.c +++ b/drivers/gpu/drm/amd/display/dc/resource/dce100/dce100_resource.c @@ -29,6 +29,7 @@ #include "stream_encoder.h" #include "resource.h" +#include "signal_types.h" #include "clk_mgr.h" #include "include/irq_service_interface.h" #include "dio/virtual/virtual_stream_encoder.h" @@ -992,6 +993,12 @@ struct stream_encoder *dce100_find_first_free_match_stream_enc_for_link( for (i = 0; i < pool->stream_enc_count; i++) { if (!res_ctx->is_stream_enc_acquired[i] && pool->stream_enc[i]) { + /* DP/MST needs a digital encoder; skip analog/no-DP encoders */ + if (dc_is_dp_signal(stream->signal) && + (!pool->stream_enc[i]->funcs || + !pool->stream_enc[i]->funcs->dp_set_stream_attribute)) + continue; + /* Store first available for MST second display * in daisy chain use case */ @@ -1014,7 +1021,7 @@ struct stream_encoder *dce100_find_first_free_match_stream_enc_for_link( * required for non DP connectors. */ - if (j >= 0 && link->connector_signal == SIGNAL_TYPE_DISPLAY_PORT) + if (j >= 0 && dc_is_dp_signal(stream->signal)) return pool->stream_enc[j]; return NULL; -- 2.55.0
