drm/amd/display: Add null checker before access structs

Checks null pointer before accessing various structs.

This fixes 5 NULL_RETURNS issues reported by Coverity.
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dml2/dml21/dml21_utils.c

@@ -360,6 +360,8 @@ static struct dc_plane_state *dml21_add_phantom_plane(struct dml2_context *dml_c
 	struct dc_plane_state *phantom_plane;
 
 	phantom_plane = dml_ctx->config.svp_pstate.callbacks.create_phantom_plane(dc, context, main_plane);
+	if (!phantom_plane)
+		return NULL;
 
 	phantom_plane->format = main_plane->format;
 	phantom_plane->rotation = main_plane->rotation;

drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_pmo/dml2_pmo_dcn4_fams2.c

@@ -1082,12 +1082,17 @@ static bool is_timing_group_schedulable(
 
 	/* init allow start and end lines for timing group */
 	stream_method_fams2_meta = get_per_method_common_meta(pmo, per_stream_pstate_strategy[base_stream_idx], base_stream_idx);
+	if (!stream_method_fams2_meta)
+		return false;
+
 	group_fams2_meta->allow_start_otg_vline = stream_method_fams2_meta->allow_start_otg_vline;
 	group_fams2_meta->allow_end_otg_vline = stream_method_fams2_meta->allow_end_otg_vline;
 	group_fams2_meta->period_us = stream_method_fams2_meta->period_us;
 	for (i = base_stream_idx + 1; i < display_cfg->display_config.num_streams; i++) {
 		if (is_bit_set_in_bitfield(pmo->scratch.pmo_dcn4.synchronized_timing_group_masks[timing_group_idx], i)) {
 			stream_method_fams2_meta = get_per_method_common_meta(pmo, per_stream_pstate_strategy[i], i);
+			if (!stream_method_fams2_meta)
+				continue;
 
 			if (group_fams2_meta->allow_start_otg_vline < stream_method_fams2_meta->allow_start_otg_vline) {
 				/* set group allow start to larger otg vline */

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

@@ -2628,7 +2628,7 @@ static bool dcn20_resource_construct(
 		ranges.writer_wm_sets[0].max_drain_clk_mhz = PP_SMU_WM_SET_RANGE_CLK_UNCONSTRAINED_MAX;
 
 		/* Notify PP Lib/SMU which Watermarks to use for which clock ranges */
-		if (pool->base.pp_smu->nv_funcs.set_wm_ranges)
+		if (pool->base.pp_smu && pool->base.pp_smu->nv_funcs.set_wm_ranges)
 			pool->base.pp_smu->nv_funcs.set_wm_ranges(&pool->base.pp_smu->nv_funcs.pp_smu, &ranges);
 	}
 

drivers/gpu/drm/amd/display/dc/resource/dcn201/dcn201_resource.c

@@ -795,11 +795,13 @@ static struct link_encoder *dcn201_link_encoder_create(
 {
 	struct dcn20_link_encoder *enc20 =
 		kzalloc(sizeof(struct dcn20_link_encoder), GFP_ATOMIC);
-	struct dcn10_link_encoder *enc10 = &enc20->enc10;
+	struct dcn10_link_encoder *enc10;
 
 	if (!enc20)
 		return NULL;
 
+	enc10 = &enc20->enc10;
+
 	dcn201_link_encoder_construct(enc20,
 			enc_init_data,
 			&link_enc_feature,