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

docs/plat/arm/arm-build-options.rst

@@ -16,6 +16,12 @@ Arm Platform Build Options
    should match the frame used by the Non-Secure image (normally the Linux
    kernel). Default is true (access to the frame is allowed).
 
+-  ``ARM_FW_CONFIG_LOAD_ENABLE``: Boolean option to enable the loading of
+   FW_CONFIG device trees from the Firmware Image Package (FIP). When enabled,
+   BL2 calls the platform specific function `arm_bl2_el3_plat_config_load`.
+   This function is responsible for loading, parsing, and validating the
+   FW_CONFIG device trees from the FIP. The option depends on RESET_TO_BL2.
+
 -  ``ARM_DISABLE_TRUSTED_WDOG``: boolean option to disable the Trusted Watchdog.
    By default, Arm platforms use a watchdog to trigger a system reset in case
    an error is encountered during the boot process (for example, when an image

fdts/tbbr_cot_descriptors.dtsi

@@ -195,6 +195,12 @@ cot {
 			hash = <&hw_config_hash>;
 		};
 
+		fw_config {
+			image-id = <FW_CONFIG_ID>;
+			parent = <&trusted_boot_fw_cert>;
+			hash = <&fw_config_hash>;
+		};
+
 		scp_bl2_image {
 			image-id = <SCP_BL2_IMAGE_ID>;
 			parent = <&scp_fw_content_cert>;

include/plat/arm/common/plat_arm.h

@@ -262,6 +262,9 @@ void arm_bl2_setup_next_ep_info(bl_mem_params_node_t *next_param_node);
 /* BL2 at EL3 functions */
 void arm_bl2_el3_early_platform_setup(void);
 void arm_bl2_el3_plat_arch_setup(void);
+#if ARM_FW_CONFIG_LOAD_ENABLE
+void arm_bl2_el3_plat_config_load(void);
+#endif /* ARM_FW_CONFIG_LOAD_ENABLE */
 
 /* BL2U utility functions */
 void arm_bl2u_early_platform_setup(struct meminfo *mem_layout,

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 @@ void bl2_el3_early_platform_setup(u_register_t arg0 __unused,
 	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.

plat/arm/common/arm_bl2_setup.c

@@ -140,6 +140,9 @@ void bl2_plat_preload_setup(void)
 
 	arm_transfer_list_dyn_cfg_init(secure_tl);
 #else
+#if ARM_FW_CONFIG_LOAD_ENABLE
+	arm_bl2_el3_plat_config_load();
+#endif /* ARM_FW_CONFIG_LOAD_ENABLE */
 	arm_bl2_dyn_cfg_init();
 #endif
 

plat/arm/common/arm_common.mk

@@ -164,6 +164,25 @@ ifneq ($(filter 1,${RESET_TO_BL31} ${RESET_TO_SP_MIN}),)
 	ENABLE_PIE			:=	1
 endif
 
+# On Arm platform, disable ARM_FW_CONFIG_LOAD_ENABLE by default.
+ARM_FW_CONFIG_LOAD_ENABLE		:= 0
+$(eval $(call assert_boolean,ARM_FW_CONFIG_LOAD_ENABLE))
+$(eval $(call add_define,ARM_FW_CONFIG_LOAD_ENABLE))
+
+# In order to enable ARM_FW_CONFIG_LOAD_ENABLE for the Arm platform, the
+# platform should be reset to BL2 (RESET_TO_BL2=1), and FW_CONFIG must be
+# specified.
+ifeq (${ARM_FW_CONFIG_LOAD_ENABLE},1)
+    ifneq (${RESET_TO_BL2},1)
+        $(error RESET_TO_BL2 must be enabled when ARM_FW_CONFIG_LOAD_ENABLE \
+            is enabled)
+    endif
+    ifeq (${FW_CONFIG},)
+        $(error FW_CONFIG must be specified when ARM_FW_CONFIG_LOAD_ENABLE \
+            is enabled)
+    endif
+endif
+
 # Disable GPT parser support, use FIP image by default
 ARM_GPT_SUPPORT			:=	0
 $(eval $(call assert_boolean,ARM_GPT_SUPPORT))