thunderbolt: Fix Thunderbolt 3 display flickering issue on 2nd hot pl…

…ug onwards

commit 583893a upstream.

Previously, on unplug events, the TMU mode was disabled first
followed by the Time Synchronization Handshake, irrespective of
whether the tb_switch_tmu_rate_write() API was successful or not.

However, this caused a problem with Thunderbolt 3 (TBT3)
devices, as the TSPacketInterval bits were always enabled by default,
leading the host router to assume that the device router's TMU was
already enabled and preventing it from initiating the Time
Synchronization Handshake. As a result, TBT3 monitors experienced
display flickering from the second hot plug onwards.

To address this issue, we have modified the code to only disable the
Time Synchronization Handshake during TMU disable if the
tb_switch_tmu_rate_write() function is successful. This ensures that
the TBT3 devices function correctly and eliminates the display
flickering issue.

Co-developed-by: Sanath S <Sanath.S@amd.com>
Signed-off-by: Sanath S <Sanath.S@amd.com>
Signed-off-by: Sanjay R Mehta <sanju.mehta@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
[ USB4v2 introduced support for uni-directional TMU mode as part of
  d49b4f0 ("thunderbolt: Add support for enhanced uni-directional TMU mode")
  This is not a stable candidate commit, so adjust the code for backport. ]
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/thunderbolt/tmu.c

@@ -415,7 +415,8 @@ int tb_switch_tmu_disable(struct tb_switch *sw)
 		 * uni-directional mode and we don't want to change it's TMU
 		 * mode.
 		 */
-		tb_switch_tmu_rate_write(sw, TB_SWITCH_TMU_RATE_OFF);
+		ret = tb_switch_tmu_rate_write(sw, TB_SWITCH_TMU_RATE_OFF);
+			return ret;
 
 		tb_port_tmu_time_sync_disable(up);
 		ret = tb_port_tmu_time_sync_disable(down);