drm/amd/display: Fix Z8 support configurations

[Why]
It's not supported in multi-display, but it is supported in 2nd eDP
screen only.

[How]
Remove multi display support, restrict number of planes for all
z-states support, but still allow Z8 if we're not using PWRSEQ0.
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dml/dcn20/dcn20_fpu.c

@@ -949,7 +949,6 @@ static enum dcn_zstate_support_state  decide_zstate_support(struct dc *dc, struc
 	int plane_count;
 	int i;
 	unsigned int optimized_min_dst_y_next_start_us;
-	bool allow_z8 = context->bw_ctx.dml.vba.StutterPeriod > 1000.0;
 
 	plane_count = 0;
 	optimized_min_dst_y_next_start_us = 0;
@@ -974,6 +973,8 @@ static enum dcn_zstate_support_state  decide_zstate_support(struct dc *dc, struc
 	else if (context->stream_count == 1 &&  context->streams[0]->signal == SIGNAL_TYPE_EDP) {
 		struct dc_link *link = context->streams[0]->sink->link;
 		struct dc_stream_status *stream_status = &context->stream_status[0];
+		bool allow_z8 = context->bw_ctx.dml.vba.StutterPeriod > 1000.0;
+		bool is_pwrseq0 = link->link_index == 0;
 
 		if (dc_extended_blank_supported(dc)) {
 			for (i = 0; i < dc->res_pool->pipe_count; i++) {
@@ -986,18 +987,17 @@ static enum dcn_zstate_support_state  decide_zstate_support(struct dc *dc, struc
 				}
 			}
 		}
-		/* zstate only supported on PWRSEQ0  and when there's <2 planes*/
-		if (link->link_index != 0 || stream_status->plane_count > 1)
+
+		/* Don't support multi-plane configurations */
+		if (stream_status->plane_count > 1)
 			return DCN_ZSTATE_SUPPORT_DISALLOW;
 
-		if (context->bw_ctx.dml.vba.StutterPeriod > 5000.0 || optimized_min_dst_y_next_start_us > 5000)
+		if (is_pwrseq0 && (context->bw_ctx.dml.vba.StutterPeriod > 5000.0 || optimized_min_dst_y_next_start_us > 5000))
 			return DCN_ZSTATE_SUPPORT_ALLOW;
-		else if (link->psr_settings.psr_version == DC_PSR_VERSION_1 && !link->panel_config.psr.disable_psr)
+		else if (is_pwrseq0 && link->psr_settings.psr_version == DC_PSR_VERSION_1 && !link->panel_config.psr.disable_psr)
 			return allow_z8 ? DCN_ZSTATE_SUPPORT_ALLOW_Z8_Z10_ONLY : DCN_ZSTATE_SUPPORT_ALLOW_Z10_ONLY;
 		else
 			return allow_z8 ? DCN_ZSTATE_SUPPORT_ALLOW_Z8_ONLY : DCN_ZSTATE_SUPPORT_DISALLOW;
-	} else if (allow_z8) {
-		return DCN_ZSTATE_SUPPORT_ALLOW_Z8_ONLY;
 	} else {
 		return DCN_ZSTATE_SUPPORT_DISALLOW;
 	}