From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Andriy Korud <a.korud@gmail.com>,
	Alex Deucher <alexander.deucher@amd.com>
Subject: [PATCH 6.18 382/675] drm/amd/display: dce100: skip non-DP stream encoders for DP MST
Date: Thu, 30 Jul 2026 16:11:52 +0200
Message-ID: <20260730141453.254439659@linuxfoundation.org>
In-Reply-To: <20260730141445.110192266@linuxfoundation.org>
References: <20260730141445.110192266@linuxfoundation.org>
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6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andriy Korud <a.korud@gmail.com>

commit d340cba0df4cf327c7e89c7c1a4e79d4771d7dd5 upstream.

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 <a.korud@gmail.com>
Closes: https://gitlab.freedesktop.org/drm/amd/-/work_items/5162
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 28ec64943e3ee4d9b8d30cea61e380f1429953a8)
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/gpu/drm/amd/display/dc/resource/dce100/dce100_resource.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/amd/display/dc/resource/dce100/dce100_resource.c
+++ b/drivers/gpu/drm/amd/display/dc/resource/dce100/dce100_resource.c
@@ -957,6 +957,11 @@ struct stream_encoder *dce100_find_first
 	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
 			 */
@@ -980,7 +985,7 @@ struct stream_encoder *dce100_find_first
 	 * 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;