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diff --git a/docs/porting-guide.rst b/docs/porting-guide.rst index 2e2cc4f7..84bd2cd4 100644 --- a/docs/porting-guide.rst +++ b/docs/porting-guide.rst @@ -1643,6 +1643,70 @@ element in the boot sequence. If there are no more boot sources then it must return 0, otherwise it must return 1. The default implementation of this always returns 0. +Boot Loader Stage 2 (BL2) at EL3 +-------------------------------- + +When the platform has a non-TF Boot ROM it is desirable to jump +directly to BL2 instead of TF BL1. In this case BL2 is expected to +execute at EL3 instead of executing at EL1. Refer to the `Firmware +Design`_ for more information. + +All mandatory functions of BL2 must be implemented, except the functions +bl2\_early\_platform\_setup and bl2\_el3\_plat\_arch\_setup, because +their work is done now by bl2\_el3\_early\_platform\_setup and +bl2\_el3\_plat\_arch\_setup. These functions should generally implement +the bl1\_plat\_xxx() and bl2\_plat\_xxx() functionality combined. + + +Function : bl2\_el3\_early\_platform\_setup() [mandatory] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + Argument : u_register_t, u_register_t, u_register_t, u_register_t + Return : void + +This function executes with the MMU and data caches disabled. It is only called +by the primary CPU. This function receives four parameters which can be used +by the platform to pass any needed information from the Boot ROM to BL2. + +On ARM standard platforms, this function does the following: + +- Initializes a UART (PL011 console), which enables access to the ``printf`` + family of functions in BL2. + +- Initializes the storage abstraction layer used to load further bootloader + images. It is necessary to do this early on platforms with a SCP\_BL2 image, + since the later ``bl2_platform_setup`` must be done after SCP\_BL2 is loaded. + +- Initializes the private variables that define the memory layout used. + +Function : bl2\_el3\_plat\_arch\_setup() [mandatory] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + Argument : void + Return : void + +This function executes with the MMU and data caches disabled. It is only called +by the primary CPU. + +The purpose of this function is to perform any architectural initialization +that varies across platforms. + +On ARM standard platforms, this function enables the MMU. + +Function : bl2\_el3\_plat\_prepare\_exit() [optional] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + Argument : void + Return : void + +This function is called prior to exiting BL2 and run the next image. +It should be used to perform platform specific clean up or bookkeeping +operations before transferring control to the next image. This function +runs with MMU disabled. + FWU Boot Loader Stage 2 (BL2U) ------------------------------ |