On Sun, Jul 12, 2026 at 11:39 AM Andriy Korud <[email protected]> wrote:
>
> From d37cbde6a3b3e57a5dc794514e77fc66e7fa8943 Mon Sep 17 00:00:00 2001
> From: Andriy Korud <[email protected]>
> Date: Fri, 10 Jul 2026 12:36:59 +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 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, 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
>
> Signed-off-by: Andriy Korud <[email protected]>
> Closes: https://gitlab.freedesktop.org/drm/amd/-/work_items/5162
I've manually fixed this up, but please use git send email in the
future to avoid having the patch get mangled.
Thanks!
Alex
> ---
> .../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
