disp: msm: dp: avoid use of mst_lock in hpd callbacks

DP MST driver registers bridge callback functions with the DRM framework.
mst_lock is used for synchronization of the mst bridge functions. These
functions call into dp_display where a session lock is obtained for
the display. HPD callbacks, on the other hand, are first handled by
dp_display. During these callbacks, dp_display takes a session lock
first before calling into DP MST driver layer. Currently, the DP MST
layer waits on mst_lock which can result in a deadlock.

This change removes the usage of mst_lock inside hpd callback functions
and just uses the session lock for synchronization.

Change-Id: I7ec338004eef43ac0f1e1f092463e9915cd60684
Signed-off-by: Rajkumar Subbiah <[email protected]>

msm/dp/dp_mst_drm.c

@@ -2163,11 +2163,8 @@ static int dp_mst_display_set_mgr_state(void *dp_display, bool state,
 	 * on hpd_low, set_mgr_state is called after hotplug event is sent and
 	 * the session_state was already updated prior to that.
 	 */
-	if (state) {
-		mutex_lock(&mst->mst_lock);
+	if (state)
 		mst->mst_session_state = state;
-		mutex_unlock(&mst->mst_lock);
-	}
 
 	if (info && !info->mst_protocol) {
 		if (state) {
@@ -2201,11 +2198,8 @@ static void dp_mst_display_hpd(void *dp_display, bool hpd_status)
 	 * session state should be unset here for the connection status to be
 	 * updated accordingly.
 	 */
-	if (!hpd_status) {
-		mutex_lock(&mst->mst_lock);
+	if (!hpd_status)
 		mst->mst_session_state = hpd_status;
-		mutex_unlock(&mst->mst_lock);
-	}
 
 	dp_mst_hpd_event_notify(mst, hpd_status);
 }