drm/amd/display: Screen corruption on dual displays (DP+USB-C)

[why]
Current pipe merge and split logic only supports cases where new
dc_state is allocated and relies on dc->current_state to gather
information from previous dc_state.

Calls to validate_bandwidth on UPDATE_TYPE_MED would cause an issue
because there is no new dc_state allocated, and data in
dc->current_state would be overwritten during pipe merge.

[how]
Only allow validate_bandwidth when new dc_state space is created.
Signed-off-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc.c

@@ -2636,7 +2636,7 @@ void dc_commit_updates_for_stream(struct dc *dc,
 
 	copy_stream_update_to_stream(dc, context, stream, stream_update);
 
-	if (update_type > UPDATE_TYPE_FAST) {
+	if (update_type >= UPDATE_TYPE_FULL) {
 		if (!dc->res_pool->funcs->validate_bandwidth(dc, context, false)) {
 			DC_ERROR("Mode validation failed for stream update!\n");
 			dc_release_state(context);

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c

@@ -3209,6 +3209,9 @@ static noinline bool dcn20_validate_bandwidth_fp(struct dc *dc,
 	context->bw_ctx.dml.soc.allow_dram_clock_one_display_vactive =
 		dc->debug.enable_dram_clock_change_one_display_vactive;
 
+	/*Unsafe due to current pipe merge and split logic*/
+	ASSERT(context != dc->current_state);
+
 	if (fast_validate) {
 		return dcn20_validate_bandwidth_internal(dc, context, true);
 	}

drivers/gpu/drm/amd/display/dc/dcn21/dcn21_resource.c

@@ -1184,6 +1184,9 @@ bool dcn21_validate_bandwidth(struct dc *dc, struct dc_state *context,
 
 	BW_VAL_TRACE_COUNT();
 
+	/*Unsafe due to current pipe merge and split logic*/
+	ASSERT(context != dc->current_state);
+
 	out = dcn20_fast_validate_bw(dc, context, pipes, &pipe_cnt, pipe_split_from, &vlevel);
 
 	if (pipe_cnt == 0)