feat(arm): add support for loading CONFIG from BL2

This commit introduces a new ARM platform-specific build option called
`ARM_FW_CONFIG_LOAD_ENABLE`. This option enables the loading of the
`fw_config` device tree when resetting to the BL2 scenario.

Additionally, the FW_CONFIG image reference has been added to the
fdts/tbbr_cot_descriptors.dtsi file in order to use in the scenario of
RESET_TO_BL2.

Signed-off-by: Divin Raj <divin.raj@arm.com>
Change-Id: I11de497b7dbb1386ed84d939d6fd2a11856e9e1b
diff --git a/plat/arm/common/arm_bl2_el3_setup.c b/plat/arm/common/arm_bl2_el3_setup.c
index 01e0db0..869830d 100644
--- a/plat/arm/common/arm_bl2_el3_setup.c
+++ b/plat/arm/common/arm_bl2_el3_setup.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2023, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2024, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -8,6 +8,8 @@
 
 #include <drivers/generic_delay_timer.h>
 #include <drivers/partition/partition.h>
+#include <lib/fconf/fconf.h>
+#include <lib/fconf/fconf_dyn_cfg_getter.h>
 #include <plat/arm/common/plat_arm.h>
 #include <plat/common/platform.h>
 #include <platform_def.h>
@@ -64,6 +66,43 @@
 	generic_delay_timer_init();
 }
 
+#if ARM_FW_CONFIG_LOAD_ENABLE
+/*************************************************************************************
+ * FW CONFIG load function for BL2 when RESET_TO_BL2=1 && ARM_FW_CONFIG_LOAD_ENABLE=1
+ *************************************************************************************/
+void arm_bl2_el3_plat_config_load(void)
+{
+	int ret;
+	const struct dyn_cfg_dtb_info_t *fw_config_info;
+
+	/* Set global DTB info for fixed fw_config information */
+	set_config_info(PLAT_FW_CONFIG_BASE, ~0UL, PLAT_FW_CONFIG_MAX_SIZE, FW_CONFIG_ID);
+
+	/* Fill the device tree information struct with the info from the config dtb */
+	ret = fconf_load_config(FW_CONFIG_ID);
+	if (ret < 0) {
+		ERROR("Loading of FW_CONFIG failed %d\n", ret);
+		plat_error_handler(ret);
+	}
+
+	/*
+	 * FW_CONFIG loaded successfully. Check the FW_CONFIG device tree parsing
+	 * is successful.
+	 */
+	fw_config_info = FCONF_GET_PROPERTY(dyn_cfg, dtb, FW_CONFIG_ID);
+	if (fw_config_info == NULL) {
+		ret = -1;
+		ERROR("Invalid FW_CONFIG address\n");
+		plat_error_handler(ret);
+	}
+	ret = fconf_populate_dtb_registry(fw_config_info->config_addr);
+	if (ret < 0) {
+		ERROR("Parsing of FW_CONFIG failed %d\n", ret);
+		plat_error_handler(ret);
+	}
+}
+#endif /* ARM_FW_CONFIG_LOAD_ENABLE */
+
 /*******************************************************************************
  * Perform the very early platform specific architectural setup here. At the
  * moment this is only initializes the mmu in a quick and dirty way.