drm/amd/display: Add null checks before accessing struct elements

[WHAT]
1. is_pwrseq0 needs to check link before accessing link->link_index.
2. context is checked before accessing its bw_ctx.dml2
3. clk_mgr_base->bw_params is checked before clk_table.num_entries_per_cl

This fixes 4 REVERSE_INULL issues reported by Coverity.
Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Hung <alex.hung@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/clk_mgr/dcn32/dcn32_clk_mgr.c

@@ -163,9 +163,14 @@ void dcn32_init_clocks(struct clk_mgr *clk_mgr_base)
 {
 	struct clk_mgr_internal *clk_mgr = TO_CLK_MGR_INTERNAL(clk_mgr_base);
 	unsigned int num_levels;
-	struct clk_limit_num_entries *num_entries_per_clk = &clk_mgr_base->bw_params->clk_table.num_entries_per_clk;
+	struct clk_limit_num_entries *num_entries_per_clk;
 	unsigned int i;
 
+	if (!clk_mgr_base->bw_params)
+		return;
+
+	num_entries_per_clk = &clk_mgr_base->bw_params->clk_table.num_entries_per_clk;
+
 	memset(&(clk_mgr_base->clks), 0, sizeof(struct dc_clocks));
 	clk_mgr_base->clks.p_state_change_support = true;
 	clk_mgr_base->clks.prev_p_state_change_support = true;
@@ -173,9 +178,6 @@ void dcn32_init_clocks(struct clk_mgr *clk_mgr_base)
 	clk_mgr->smu_present = false;
 	clk_mgr->dpm_present = false;
 
-	if (!clk_mgr_base->bw_params)
-		return;
-
 	if (!clk_mgr_base->force_smu_not_present && dcn30_smu_get_smu_version(clk_mgr, &clk_mgr->smu_ver))
 		clk_mgr->smu_present = true;
 

drivers/gpu/drm/amd/display/dc/clk_mgr/dcn401/dcn401_clk_mgr.c

@@ -207,9 +207,14 @@ static void dcn401_build_wm_range_table(struct clk_mgr *clk_mgr)
 void dcn401_init_clocks(struct clk_mgr *clk_mgr_base)
 {
 	struct clk_mgr_internal *clk_mgr = TO_CLK_MGR_INTERNAL(clk_mgr_base);
-	struct clk_limit_num_entries *num_entries_per_clk = &clk_mgr_base->bw_params->clk_table.num_entries_per_clk;
+	struct clk_limit_num_entries *num_entries_per_clk;
 	unsigned int i;
 
+	if (!clk_mgr_base->bw_params)
+		return;
+
+	num_entries_per_clk = &clk_mgr_base->bw_params->clk_table.num_entries_per_clk;
+
 	memset(&(clk_mgr_base->clks), 0, sizeof(struct dc_clocks));
 	clk_mgr_base->clks.p_state_change_support = true;
 	clk_mgr_base->clks.prev_p_state_change_support = true;
@@ -217,9 +222,6 @@ void dcn401_init_clocks(struct clk_mgr *clk_mgr_base)
 	clk_mgr->smu_present = false;
 	clk_mgr->dpm_present = false;
 
-	if (!clk_mgr_base->bw_params)
-		return;
-
 	if (!clk_mgr_base->force_smu_not_present && dcn30_smu_get_smu_version(clk_mgr, &clk_mgr->smu_ver))
 		clk_mgr->smu_present = true;
 

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

@@ -1084,7 +1084,7 @@ static enum dcn_zstate_support_state  decide_zstate_support(struct dc *dc, struc
 		struct dc_stream_status *stream_status = &context->stream_status[0];
 		int minmum_z8_residency = dc->debug.minimum_z8_residency_time > 0 ? dc->debug.minimum_z8_residency_time : 1000;
 		bool allow_z8 = context->bw_ctx.dml.vba.StutterPeriod > (double)minmum_z8_residency;
-		bool is_pwrseq0 = link->link_index == 0;
+		bool is_pwrseq0 = (link && link->link_index == 0);
 		bool is_psr = (link && (link->psr_settings.psr_version == DC_PSR_VERSION_1 ||
 						link->psr_settings.psr_version == DC_PSR_VERSION_SU_1) && !link->panel_config.psr.disable_psr);
 		bool is_replay = link && link->replay_settings.replay_feature_enabled;

drivers/gpu/drm/amd/display/dc/dml2/dml2_wrapper.c

@@ -687,12 +687,14 @@ static bool dml2_validate_and_build_resource(const struct dc *in_dc, struct dc_s
 
 static bool dml2_validate_only(struct dc_state *context)
 {
-	struct dml2_context *dml2 = context->bw_ctx.dml2;
+	struct dml2_context *dml2;
 	unsigned int result = 0;
 
 	if (!context || context->stream_count == 0)
 		return true;
 
+	dml2 = context->bw_ctx.dml2;
+
 	/* Zero out before each call before proceeding */
 	memset(&dml2->v20.scratch, 0, sizeof(struct dml2_wrapper_scratch));
 	memset(&dml2->v20.dml_core_ctx.policy, 0, sizeof(struct dml_mode_eval_policy_st));