drm/amd/display: Reject overlay plane configurations in multi-display scenarios

[Why]
These aren't stable on some platform configurations when driving
multiple displays, especially on higher resolution.

In particular the delay in asserting p-state and validating from
x86 outweights any power or performance benefit from the hardware
composition.

Under some configurations this will manifest itself as extreme stutter
or unresponsiveness especially when combined with cursor movement.

[How]
Disable these for now. Exposing overlays to userspace doesn't guarantee
that they'll be able to use them in any and all configurations and it's
part of the DRM contract to have userspace gracefully handle validation
failures when they occur.

Valdiation occurs as part of DC and this in particular affects RV, so
disable this in dcn10_global_validation.
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Hersen Wu <hersenxs.wu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_resource.c

@@ -1213,6 +1213,7 @@ static enum dc_status dcn10_validate_global(struct dc *dc, struct dc_state *cont
 	bool video_large = false;
 	bool desktop_large = false;
 	bool dcc_disabled = false;
+	bool mpo_enabled = false;
 
 	for (i = 0; i < context->stream_count; i++) {
 		if (context->stream_status[i].plane_count == 0)
@@ -1221,6 +1222,9 @@ static enum dc_status dcn10_validate_global(struct dc *dc, struct dc_state *cont
 		if (context->stream_status[i].plane_count > 2)
 			return DC_FAIL_UNSUPPORTED_1;
 
+		if (context->stream_status[i].plane_count > 1)
+			mpo_enabled = true;
+
 		for (j = 0; j < context->stream_status[i].plane_count; j++) {
 			struct dc_plane_state *plane =
 				context->stream_status[i].plane_states[j];
@@ -1244,6 +1248,10 @@ static enum dc_status dcn10_validate_global(struct dc *dc, struct dc_state *cont
 		}
 	}
 
+	/* Disable MPO in multi-display configurations. */
+	if (context->stream_count > 1 && mpo_enabled)
+		return DC_FAIL_UNSUPPORTED_1;
+
 	/*
 	 * Workaround: On DCN10 there is UMC issue that causes underflow when
 	 * playing 4k video on 4k desktop with video downscaled and single channel