[U-Boot] [PATCH v2] arm: spl: Allow board_init_r() to run with a larger stack

[Albert ARIBAUD <albert.u.boot@aribaud.net>]

Hello Simon,

On Mon, 26 Jan 2015 08:34:21 -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

lowlevel_init() does not have a stack for all ARM CPUs, e.g. for
arm926ejs it has none; and I don't see any code in this patch that
provides one. If we need lowlevel_init to have a stack, then this stack
should be set up in crt0.S and lowlevel_init called from there (which
I would be fine with, btw).

> 	- 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
> 
> Signed-off-by: Simon Glass <sjg@chromium.org>
> For version 1:
> Acked-by: Albert ARIBAUD <albert.u.boot@aribaud.net>
> Reviewed-by: Stefan Roese <sr@denx.de>
> Tested-by: Bo Shen <voice.shen@atmel.com>
> Acked-by: Bo Shen <voice.shen@atmel.com>
> Acked-by: Heiko Schocher <hs@denx.de>
> Tested-by: Heiko Schocher <hs@denx.de>
> ---
> 
> Changes in v2:
> - Move docs to top-level README file and expand them to cover U-Boot proper
> - Add Kconfig settings
> 
>  Kconfig             | 18 ++++++++++++++
>  README              | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  arch/arm/lib/crt0.S | 13 +++++++---
>  common/spl/spl.c    | 35 +++++++++++++++++++++++++++
>  4 files changed, 131 insertions(+), 3 deletions(-)
> 
> diff --git a/Kconfig b/Kconfig
> index 4157da3..8398bcd 100644
> --- a/Kconfig
> +++ b/Kconfig
> @@ -92,6 +92,24 @@ config SPL
>  	help
>  	  If you want to build SPL as well as the normal image, say Y.
>  
> +config CONFIG_SPL_STACK_R
> +	depends on SPL
> +	bool "Enable SDRAM location for SPL stack"
> +	help
> +	  SPL starts off execution in SRAM and thus typically has only a small
> +	  stack available. Since SPL sets up DRAM while in its board_init_f()
> +	  function, it is possible for the stack to move there before
> +	  board_init_r() is reached. This option enables a special SDRAM
> +	  location for the SPL stack. U-Boot SPL switches to this after
> +	  board_init_f() completes, and before board_init_r() starts.
> +
> +config CONFIG_SPL_STACK_R_ADDR
> +	depends on CONFIG_SPL_STACK_R
> +	hex "SDRAM location for SPL stack"
> +	help
> +	  Specify the address in SDRAM for the SPL stack. This will be set up
> +	  before board_init_r() is called.
> +
>  config TPL
>  	bool
>  	depends on SPL && SUPPORT_TPL
> diff --git a/README b/README
> index fefa71c..7b48cda 100644
> --- a/README
> +++ b/README
> @@ -273,6 +273,74 @@ run some of U-Boot's tests.
>  See board/sandbox/README.sandbox 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). At present SPL
> +mostly uses a separate code path, but the funtion 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 starts with start.S with three functions called during init after
> +that. The purpose and limitations of each is described below.
> +
> +lowlevel_init():
> +	- purpose: essential init to permit execution to reach board_init_f()
> +	- no global_data or BSS, 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
> +	- 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
> +	- 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. 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 and
> +		CONFIG_SPL_STACK_R_ADDR 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
> +
> +
> +
>  Configuration Options:
>  ----------------------
>  
> diff --git a/arch/arm/lib/crt0.S b/arch/arm/lib/crt0.S
> index 22df3e5..7939ced 100644
> --- a/arch/arm/lib/crt0.S
> +++ b/arch/arm/lib/crt0.S
> @@ -113,7 +113,14 @@ here:
>  /* Set up final (full) environment */
>  
>  	bl	c_runtime_cpu_setup	/* we still call old routine here */
> -
> +#endif
> +#if !defined(CONFIG_SPL_BUILD) || defined(CONFIG_SPL_FRAMEWORK)
> +# ifdef CONFIG_SPL_BUILD
> +	/* Use a DRAM stack for the rest of SPL, if requested */
> +	bl	spl_relocate_stack_gd
> +	cmp	r0, #0
> +	movne	sp, r0
> +# endif
>  	ldr	r0, =__bss_start	/* this is auto-relocated! */
>  	ldr	r1, =__bss_end		/* this is auto-relocated! */
>  
> @@ -124,9 +131,10 @@ clbss_l:cmp	r0, r1			/* while not at end of BSS */
>  	addlo	r0, r0, #4		/* move to next */
>  	blo	clbss_l
>  
> +#if ! defined(CONFIG_SPL_BUILD)
>  	bl coloured_LED_init
>  	bl red_led_on
> -
> +#endif
>  	/* call board_init_r(gd_t *id, ulong dest_addr) */
>  	mov     r0, r9                  /* gd_t */
>  	ldr	r1, [r9, #GD_RELOCADDR]	/* dest_addr */
> @@ -134,7 +142,6 @@ clbss_l:cmp	r0, r1			/* while not at end of BSS */
>  	ldr	pc, =board_init_r	/* this is auto-relocated! */
>  
>  	/* we should not return here. */
> -
>  #endif
>  
>  ENDPROC(_main)
> diff --git a/common/spl/spl.c b/common/spl/spl.c
> index 1826c47..78bb279 100644
> --- a/common/spl/spl.c
> +++ b/common/spl/spl.c
> @@ -276,3 +276,38 @@ void preloader_console_init(void)
>  	spl_display_print();
>  #endif
>  }
> +
> +/**
> + * spl_relocate_stack_gd() - Relocate stack ready for board_init_r() execution
> + *
> + * Sometimes board_init_f() runs with a stack in SRAM but we want to use SDRAM
> + * for the main board_init_r() execution. This is typically because we need
> + * more stack space for things like the MMC sub-system.
> + *
> + * This function calculates the stack position, copies the global_data into
> + * place and returns the new stack position. The caller is responsible for
> + * setting up the sp register.
> + *
> + * @return new stack location, or 0 to use the same stack
> + */
> +ulong spl_relocate_stack_gd(void)
> +{
> +#ifdef CONFIG_SPL_STACK_R
> +	gd_t *new_gd;
> +	ulong ptr;
> +
> +	/* Get stack position: use 8-byte alignment for ABI compliance */
> +	ptr = CONFIG_SPL_STACK_R - sizeof(gd_t);
> +	ptr &= ~7;
> +	new_gd = (gd_t *)ptr;
> +	memcpy(new_gd, (void *)gd, sizeof(gd_t));
> +	gd = new_gd;
> +
> +	/* Clear the BSS. */
> +	memset(__bss_start, 0, __bss_end - __bss_start);
> +
> +	return ptr;
> +#else
> +	return 0;
> +#endif
> +}
> -- 
> 2.2.0.rc0.207.ga3a616c
> 



Amicalement,
-- 
Albert.