From 92bd92c44d0d9be5dcbcda315b4be4b909ed9740 Mon Sep 17 00:00:00 2001
From: Rajkumar Subbiah <rsubbia@codeaurora.org>
Date: Tue, 6 Jul 2021 08:30:34 -0700
Subject: [PATCH] drm/dp_mst: Fix return code on sideband message failure
Git-commit: 92bd92c44d0d9be5dcbcda315b4be4b909ed9740
Patch-mainline: v5.15-rc1
References: git-fixes stable-5.14.6

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@vger.kernel.org> # v5.5+
Signed-off-by: Rajkumar Subbiah <rsubbia@codeaurora.org>
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1625585434-9562-1-git-send-email-khsieh@codeaurora.org
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 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 ad0795afc21c..86d13d6bc463 100644
--- 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(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 (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;
 	}
 
-- 
2.26.2