Move this section to rst, changing it just enough so that it builds.
Signed-off-by: Simon Glass sjg@chromium.org ---
(no changes since v1)
README | 81 ------------------------------------- doc/develop/index.rst | 1 + doc/develop/init.rst | 92 +++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 93 insertions(+), 81 deletions(-) create mode 100644 doc/develop/init.rst
diff --git a/README b/README index 5115d28fac1..5a5b93fecb8 100644 --- a/README +++ b/README @@ -134,87 +134,6 @@ run some of U-Boot's tests. See doc/arch/sandbox/sandbox.rst for more details.
-Board Initialisation Flow: --------------------------- - -This is the intended start-up flow for boards. This should apply for both -SPL and U-Boot proper (i.e. they both follow the same rules). - -Note: "SPL" stands for "Secondary Program Loader," which is explained in -more detail later in this file. - -At present, SPL mostly uses a separate code path, but the function names -and roles of each function are the same. Some boards or architectures -may not conform to this. At least most ARM boards which use -CONFIG_SPL_FRAMEWORK conform to this. - -Execution typically starts with an architecture-specific (and possibly -CPU-specific) start.S file, such as: - - - arch/arm/cpu/armv7/start.S - - arch/powerpc/cpu/mpc83xx/start.S - - arch/mips/cpu/start.S - -and so on. From there, three functions are called; the purpose and -limitations of each of these functions are described below. - -lowlevel_init(): - - purpose: essential init to permit execution to reach board_init_f() - - no global_data or BSS - - there is no stack (ARMv7 may have one but it will soon be removed) - - must not set up SDRAM or use console - - must only do the bare minimum to allow execution to continue to - board_init_f() - - this is almost never needed - - return normally from this function - -board_init_f(): - - purpose: set up the machine ready for running board_init_r(): - i.e. SDRAM and serial UART - - global_data is available - - stack is in SRAM - - BSS is not available, so you cannot use global/static variables, - only stack variables and global_data - - Non-SPL-specific notes: - - dram_init() is called to set up DRAM. If already done in SPL this - can do nothing - - SPL-specific notes: - - you can override the entire board_init_f() function with your own - version as needed. - - preloader_console_init() can be called here in extremis - - should set up SDRAM, and anything needed to make the UART work - - there is no need to clear BSS, it will be done by crt0.S - - for specific scenarios on certain architectures an early BSS *can* - be made available (via CONFIG_SPL_EARLY_BSS by moving the clearing - of BSS prior to entering board_init_f()) but doing so is discouraged. - Instead it is strongly recommended to architect any code changes - or additions such to not depend on the availability of BSS during - board_init_f() as indicated in other sections of this README to - maintain compatibility and consistency across the entire code base. - - must return normally from this function (don't call board_init_r() - directly) - -Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then at -this point the stack and global_data are relocated to below -CONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top of -memory. - -board_init_r(): - - purpose: main execution, common code - - global_data is available - - SDRAM is available - - BSS is available, all static/global variables can be used - - execution eventually continues to main_loop() - - Non-SPL-specific notes: - - U-Boot is relocated to the top of memory and is now running from - there. - - SPL-specific notes: - - stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined - The following options need to be configured:
- CPU Type: Define exactly one, e.g. CONFIG_MPC85XX. diff --git a/doc/develop/index.rst b/doc/develop/index.rst index 0d0e60ab56c..da9643dca14 100644 --- a/doc/develop/index.rst +++ b/doc/develop/index.rst @@ -38,6 +38,7 @@ Implementation distro driver-model/index environment + init expo cedit event diff --git a/doc/develop/init.rst b/doc/develop/init.rst new file mode 100644 index 00000000000..2955d9bdbc3 --- /dev/null +++ b/doc/develop/init.rst @@ -0,0 +1,92 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +Board Initialisation Flow +------------------------- + +This is the intended start-up flow for boards. This should apply for both +SPL and U-Boot proper (i.e. they both follow the same rules). + +Note: "SPL" stands for "Secondary Program Loader," which is explained in +more detail later in this file. + +At present, SPL mostly uses a separate code path, but the function names +and roles of each function are the same. Some boards or architectures +may not conform to this. At least most ARM boards which use +CONFIG_SPL_FRAMEWORK conform to this. + +Execution typically starts with an architecture-specific (and possibly +CPU-specific) start.S file, such as: + +- arch/arm/cpu/armv7/start.S +- arch/powerpc/cpu/mpc83xx/start.S +- arch/mips/cpu/start.S + +and so on. From there, three functions are called; the purpose and +limitations of each of these functions are described below. + +lowlevel_init() +~~~~~~~~~~~~~~~ + +- purpose: essential init to permit execution to reach board_init_f() +- no global_data or BSS +- there is no stack (ARMv7 may have one but it will soon be removed) +- must not set up SDRAM or use console +- must only do the bare minimum to allow execution to continue to + board_init_f() +- this is almost never needed +- return normally from this function + +board_init_f() +~~~~~~~~~~~~~~ + +- purpose: set up the machine ready for running board_init_r(): + i.e. SDRAM and serial UART +- global_data is available +- stack is in SRAM +- BSS is not available, so you cannot use global/static variables, + only stack variables and global_data + +Non-xPL-specific notes: + + - dram_init() is called to set up DRAM. If already done in SPL this + can do nothing + +xPL-specific notes: + + - you can override the entire board_init_f() function with your own + version as needed. + - preloader_console_init() can be called here in extremis + - should set up SDRAM, and anything needed to make the UART work + - there is no need to clear BSS, it will be done by crt0.S + - for specific scenarios on certain architectures an early BSS *can* + be made available (via CONFIG_SPL_EARLY_BSS by moving the clearing + of BSS prior to entering board_init_f()) but doing so is discouraged. + Instead it is strongly recommended to architect any code changes + or additions such to not depend on the availability of BSS during + board_init_f() as indicated in other sections of this README to + maintain compatibility and consistency across the entire code base. + - must return normally from this function (don't call board_init_r() + directly) + +Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then at +this point the stack and global_data are relocated to below +CONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top of +memory. + +board_init_r() +~~~~~~~~~~~~~~ + + - purpose: main execution, common code + - global_data is available + - SDRAM is available + - BSS is available, all static/global variables can be used + - execution eventually continues to main_loop() + +Non-SPL-specific notes: + + - U-Boot is relocated to the top of memory and is now running from + there. + +SPL-specific notes: + + - stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined