Hi Albert,
On 18 January 2015 at 23:54, Albert ARIBAUD albert.u.boot@aribaud.net wrote:
Hello Simon,
On Sun, 18 Jan 2015 11:55:36 -0700, Simon Glass sjg@chromium.org wrote:
At present SPL uses a single stack, either CONFIG_SPL_STACK or CONFIG_SYS_INIT_SP_ADDR. Since some SPL features (such as MMC and environment) require a lot of stack, some boards set CONFIG_SPL_STACK to point into SDRAM. They then set up SDRAM very early, before board_init_f(), so that the larger stack can be used.
This is an abuse of lowlevel_init(). That function should only be used for essential start-up code which cannot be delayed. An example of a valid use is when only part of the SPL code is visible/executable, and the SoC must be set up so that board_init_f() can be reached. It should not be used for SDRAM init, console init, etc.
Add a CONFIG_SPL_STACK_R option, which allows the stack to be moved to a new address before board_init_r() is called in SPL.
The expected SPL flow (for CONFIG_SPL_FRAMEWORK) is now:
Execution starts with start.S. Two main functions can be provided by the board implementation. The purpose and limitations of each is described below. After that, the common board_init_r() is called to perform the SPL task.
lowlevel_init(): - purpose: essential init to permit execution to reach board_init_f() - no global_data, but there is a stack - 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 - preloader_console_init() can be called here in extremis - stack is in SRAM - should set up SDRAM, and anything needed to make the UART work - these is no need to clear BSS, it will be done by crt0.S - must return normally from this function (don't call board_init_r() directly)
Here the BSS is cleared. If CONFIG_SPL_STACK_R is defined, then at this point the stack and global_data are relocated to below that address.
board_init_r(): - purpose: main execution, common code - global_data is available - SDRAM is available - stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and points into SDRAM - preloader_console_init() can be called here - typically this is done by defining CONFIG_SPL_BOARD_INIT and then supplying a spl_board_init() function containing this call - loads U-Boot or (in falcon mode) Linux
Seems to me that now SPL and non-SPL boot sequences are mostly similar in the name, order and purpose of the functions called (which is a good thing!) so maybe this sequence should be described in a single document rather than in doc/README.SPL? Just opening the discussion; I have no strong opinion on this.
Yes that is the idea. Yes I think it would be good to documentation this more generally, although I wonder if we should wait until some boards actually support this? :-)
Regards, Simon