This is a note to let you know that I've just added the patch titled drm/dp_mst: Fix return code on sideband message failure to the 5.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drm-dp_mst-fix-return-code-on-sideband-message-failure.patch and it can be found in the queue-5.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 92bd92c44d0d9be5dcbcda315b4be4b909ed9740 Mon Sep 17 00:00:00 2001 From: Rajkumar Subbiah <rsubbia@xxxxxxxxxxxxxx> Date: Tue, 6 Jul 2021 08:30:34 -0700 Subject: drm/dp_mst: Fix return code on sideband message failure From: Rajkumar Subbiah <rsubbia@xxxxxxxxxxxxxx> commit 92bd92c44d0d9be5dcbcda315b4be4b909ed9740 upstream. Commit 2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing + selftests") 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 response. Fixes the issue by returning the proper error code. Changes in V2: -- Revise commit text as review comment -- add Fixes text Changes in V3: -- remove "unlikely" optimization Fixes: 2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing + selftests") Cc: <stable@xxxxxxxxxxxxxxx> # v5.5+ Signed-off-by: Rajkumar Subbiah <rsubbia@xxxxxxxxxxxxxx> Signed-off-by: Kuogee Hsieh <khsieh@xxxxxxxxxxxxxx> Reviewed-by: Stephen Boyd <swboyd@xxxxxxxxxxxx> Reviewed-by: Jani Nikula <jani.nikula@xxxxxxxxx> Reviewed-by: Lyude Paul <lyude@xxxxxxxxxx> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx> Link: https://patchwork.freedesktop.org/patch/msgid/1625585434-9562-1-git-send-email-khsieh@xxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/gpu/drm/drm_dp_mst_topology.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -2872,11 +2872,13 @@ static int process_single_tx_qlock(struc 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 (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; } Patches currently in stable-queue which might be from rsubbia@xxxxxxxxxxxxxx are queue-5.14/drm-dp_mst-fix-return-code-on-sideband-message-failure.patch