[U-Boot] [PATCH] arm: spl: Allow board_init_r() to run with a larger stack

[Stefan Roese <sr@denx.de>]

On 18.01.2015 19:55, Simon Glass 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
>
> Note: This patch is intended to apply over the top of Tom's SPL changes and
> this series:
>
> https://patchwork.ozlabs.org/patch/423785/
>
> Signed-off-by: Simon Glass <sjg@chromium.org>

Reviewed-by: Stefan Roese <sr@denx.de>

Thanks,
Stefan