drm/dp_mst: Fix return code on sideband message failure

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@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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index a68dc25a19c6d31718273f31f93d924a039b3ada..04e7a8d20f259401a1c7683b47bd33a14b0c3fb4 100644 (file)
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2867,11 +2867,13 @@ 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;
        }