ATF

• • • • 1、背景
      • 2、ATF編譯
      • 3、ATF的啟動
      • 4、獲取optee/uboot的跳轉地址
      • 4、總結一下ATF啟動流程

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1、背景

在vendor某些廠商的設計中，ATF并不是BOOTROM加載后的第一個啟動鏡像，可能是這樣的：
BOOTROM—>PL—>ATF—>optee—>uboot…, 在PL階段就已經將ATF/optee/uboot鏡像的load到內存了.

2、ATF編譯

由上述背景的原因，我們的ATF就不需要走BL1/BL2階段load optee/uboot鏡像到內存了，直接走BL3即可.
所以bl1和bl2目錄也無需編譯.

我們的編譯方法是在make的時候傳入RESET_TO_BL31=1參數：

make -C $DIRPATH RESET_TO_BL31=1 PLAT=xxxx clean make -C $DIRPATH RESET_TO_BL31=1 PLAT=xxx xxxx_VDK=0 xxxxxx=0 xxxxxx=0 HIGHADDR_DEVICE=1 all

3、ATF的啟動

從bl31.ld.S文件可知，ATF是從bl31_entrypoint開始啟動的

func bl31_entrypointbl bl31_early_platform_setupbl bl31_plat_arch_setupbl bl31_main

在bl31_main()函數中:

• runtime_svc_init()跳轉optee之前的準備，然后再調用bl32_init跳轉到optee，optee
  os初始化完成后再從此處回來。
• bl31_prepare_next_image_entry()跳轉uboot之前的準備，返回到bl31_entrypoint后調用b
  el3_exit跳轉到uboot, PC就不會再回此處了。下次PC再回來就是在REE進行了smc調用，那時是直接跳轉到ATF的異常向量表.

void bl31_main(void) {NOTICE("BL31: %s\n", version_string);NOTICE("BL31: %s\n", build_message);/* Perform remaining generic architectural setup from EL3 */bl31_arch_setup();/* Perform platform setup in BL31 */bl31_platform_setup();/* Initialise helper libraries */bl31_lib_init();/* Initialize the runtime services e.g. psci */INFO("BL31: Initializing runtime services\n");runtime_svc_init();/** All the cold boot actions on the primary cpu are done. We now need to* decide which is the next image (BL32 or BL33) and how to execute it.* If the SPD runtime service is present, it would want to pass control* to BL32 first in S-EL1. In that case, SPD would have registered a* function to intialize bl32 where it takes responsibility of entering* S-EL1 and returning control back to bl31_main. Once this is done we* can prepare entry into BL33 as normal.*//** If SPD had registerd an init hook, invoke it.*/if (bl32_init) {INFO("BL31: Initializing BL32\n");(*bl32_init)();}/** We are ready to enter the next EL. Prepare entry into the image* corresponding to the desired security state after the next ERET.*/bl31_prepare_next_image_entry();/** Perform any platform specific runtime setup prior to cold boot exit* from BL31*/bl31_plat_runtime_setup(); }

4、獲取optee/uboot的跳轉地址

bl31_prepare_next_image_entry()可以獲取optee/uboot的跳轉地址，該地址最終來自于platform_def.h頭文件中寫死的地址

• #define BL32_BASE (PLAT_S_DRAM_BASE + BL31_SIZE + PLAT_TRUSTED_MAILBOX_SIZE)
• #define PLAT_NS_IMAGE_BASE 0x80000000
  #define PLAT_NS_IMAGE_OFFSET (PLAT_NS_IMAGE_BASE + 0x9000000)

void bl31_prepare_next_image_entry(void) {entry_point_info_t *next_image_info;uint32_t image_type;/* Determine which image to execute next */image_type = bl31_get_next_image_type();/* Program EL3 registers to enable entry into the next EL */next_image_info = bl31_plat_get_next_image_ep_info(image_type);assert(next_image_info);assert(image_type == GET_SECURITY_STATE(next_image_info->h.attr));INFO("BL31: Preparing for EL3 exit to %s world\n",(image_type == SECURE) ? "secure" : "normal");print_entry_point_info(next_image_info);cm_init_my_context(next_image_info);cm_prepare_el3_exit(image_type); } entry_point_info_t *bl31_plat_get_next_image_ep_info(uint32_t type) {assert(sec_state_is_valid(type));if (type == NON_SECURE)return &bl33_image_ep_info;if (type == SECURE)return &bl32_image_ep_info;return NULL; }void bl31_early_platform_setup(bl31_params_t *from_bl2,void *plat_params_from_bl2) {......bl32_image_ep_info.pc = BL32_BASE;............bl33_image_ep_info.pc = plat_get_ns_image_entrypoint();bl33_image_ep_info.spsr = plat_get_spsr_for_bl33_entry();...... }unsigned long plat_get_ns_image_entrypoint(void) {return PLAT_NS_IMAGE_OFFSET; }

4、總結一下ATF啟動流程

總結

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