drm/komeda: Handle NULL pointer access code path in error case

komeda_component_get_old_state() technically can return a NULL
pointer. komeda_compiz_set_input() even warns when this happens, but
then proceeeds to use that NULL pointer to compare memory content there
agains the new state to see if it changed. In this case, it's better to
assume that the input changed as there is no old state to compare
against and thus assume the changes happen anyway.
Signed-off-by: Carsten Haitzler <carsten.haitzler@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
[Applied small spelling fixes and fix suggested by Steven Price]
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201127110054.133686-1-carsten.haitzler@foss.arm.com

drivers/gpu/drm/arm/display/komeda/komeda_pipeline_state.c

@@ -704,10 +704,10 @@ komeda_compiz_set_input(struct komeda_compiz *compiz,
 	cin->layer_alpha = dflow->layer_alpha;
 
 	old_st = komeda_component_get_old_state(&compiz->base, drm_st);
-	WARN_ON(!old_st);
 
 	/* compare with old to check if this input has been changed */
-	if (memcmp(&(to_compiz_st(old_st)->cins[idx]), cin, sizeof(*cin)))
+	if (WARN_ON(!old_st) ||
+	    memcmp(&(to_compiz_st(old_st)->cins[idx]), cin, sizeof(*cin)))
 		c_st->changed_active_inputs |= BIT(idx);
 
 	komeda_component_add_input(c_st, &dflow->input, idx);