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Subject[PATCH] drm/dp_mst: Fix return code on sideband message failure
From: Rajkumar Subbiah <>

The commit 2f015ec6eab69301fdcf54d397810d72362d7223 added some debug
code for sideband message tracing. But it seems to have unintentionally
changed the behavior on sideband message failure. It catches and returns
failure only if DRM_UT_DP is enabled. Otherwise it ignores the error code
and returns success. So on an MST unplug, the caller is unaware that the
clear payload message failed and ends up waiting for 4 seconds for the

This change fixes the issue by returning the proper error code.

Change-Id: I2887b7ca21355fe84a7968f7619d5e8199cbb0c6
Signed-off-by: Rajkumar Subbiah <>
drivers/gpu/drm/drm_dp_mst_topology.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 1590144..8d97430 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2887,11 +2887,13 @@ static int process_single_tx_qlock(struct drm_dp_mst_topology_mgr *mgr,
idx += tosend + 1;

ret = drm_dp_send_sideband_msg(mgr, up, chunk, idx);
- if (unlikely(ret) && drm_debug_enabled(DRM_UT_DP)) {
- struct drm_printer p = drm_debug_printer(DBG_PREFIX);
+ if (unlikely(ret)) {
+ if (drm_debug_enabled(DRM_UT_DP)) {
+ struct drm_printer p = drm_debug_printer(DBG_PREFIX);

- drm_printf(&p, "sideband msg failed to send\n");
- drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
+ drm_printf(&p, "sideband msg failed to send\n");
+ drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
+ }
return ret;

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a Linux Foundation Collaborative Project
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