FAILED: patch "[PATCH] drm/amdgpu/dm/dp_mst: Don't grab mst_mgr->lock when computing" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Possible dependencies:

14b651b22224 ("drm/amdgpu/dm/dp_mst: Don't grab mst_mgr->lock when computing DSC state") d3e2c664ec9a ("drm/amdgpu/dm/mst: Use the correct topology mgr pointer in amdgpu_dm_connector") 7cce4cd628be ("drm/amdgpu/mst: Stop ignoring error codes and deadlocking")
876fcc4222e1 ("drm/amd/display: Validate DSC After Enable All New CRTCs")
47519d8224ba ("Merge tag 'amd-drm-next-6.1-2022-09-08' of https://gitlab.freedesktop.org/agd5f/linux into drm-next")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 14b651b22224251b35618259da714adb0b5f10ee Mon Sep 17 00:00:00 2001
From: Lyude Paul <[email protected]>
Date: Mon, 14 Nov 2022 17:17:55 -0500
Subject: [PATCH] drm/amdgpu/dm/dp_mst: Don't grab mst_mgr->lock when computing
DSC state

Now that we've fixed the issue with using the incorrect topology manager, we're actually grabbing the topology manager's lock - and consequently deadlocking. Luckily for us though, there's actually nothing in AMD's DSC state computation code that really should need this lock. The one exception is the mutex_lock() in dm_dp_mst_is_port_support_mode(), however we grab no locks beneath &mgr->lock there so that should be fine to leave be.

Gitlab issue: https://gitlab.freedesktop.org/drm/amd/-/issues/2171

index bb4801d7625e..24d859ad4712 100644
@@ -1155,10 +1155,8 @@ int compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
 			continue;
 
 		mst_mgr = aconnector->port->mgr;
-		mutex_lock(&mst_mgr->lock);
 		ret = compute_mst_dsc_configs_for_link(state, dc_state, stream->link, vars, mst_mgr,
 						       &link_vars_start_index);
-		mutex_unlock(&mst_mgr->lock);
 		if (ret != 0)
 			return ret;
 

@@ -1215,10 +1213,8 @@ static int pre_compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
 			continue;
 
 		mst_mgr = aconnector->port->mgr;
-		mutex_lock(&mst_mgr->lock);
 		ret = compute_mst_dsc_configs_for_link(state, dc_state, stream->link, vars, mst_mgr,
 						       &link_vars_start_index);
-		mutex_unlock(&mst_mgr->lock);
 		if (ret != 0)
 			return ret;