[U-Boot-Users] Uboot-V2: ARM: towards a common start-arm.S

[Sascha Hauer <s.hauer@pengutronix.de>]

Hi,

On Mon, Mar 17, 2008 at 05:32:10PM -0500, Nishanth Menon wrote:
> Hi Sascha,
> 
> I think we dont have a seperate list for uboot-v2, 

No we have not. This is the right place ;)

> so, just wanted to
> know the opinion of having a single arch/arm/cpu/start-arm.S instead of
> multiple start-arm files. essentially providing hooks to arch,soc,board
> specific preinits can allow us to reuse major chunk of code..
> I have attached a sample start-arm.S (modified from start-arm920t.S) as
> reference.
> 
> Do let me know your comments and view as to how the initial handling can
> be made abstract enough to plug into requirements of future SOCs, boards
> etc. I am looking not to mash in #ifdef ARCH_XYZ for each of the SOC
> implementation I plan on doing.
> 
> Regards,
> Nishanth Menon

It is my plan to unify the different start.S files anyway, so good idea
;)

I'll comment on a diff to current start-arm920t.S as it's easier to see what
you actually changed.

> diff --git a/arch/arm/cpu/start-arm920t.S b/arch/arm/cpu/start-arm920t.S
> index db52ad9..a2c9ecb 100644
> --- a/arch/arm/cpu/start-arm920t.S
> +++ b/arch/arm/cpu/start-arm920t.S
> @@ -29,11 +29,7 @@
>   * @brief The very basic beginning of each CPU after reset
>   *
>   * @note
> - * This reset code can be used at least for:
> - *  - ARM920T
> - *  - i.MX1
> - *  - i.MX27
> - *  - i.MX31
> + * This reset code can be used at least for All ARM platforms
> 

I wouldn't say it works at least on all arm platforms, maybe for xscale
it's easier to have a start-xscale.S, but I haven't looked into this
very deeply. But for sure this code won't work on any non-arm platform.

>   *
>   * FIXME: Stop doxygen from parsing the text below
>   */
> @@ -134,32 +130,26 @@ reset:
>  #ifdef ARCH_HAS_INIT_LOWLEVEL
>  	bl arch_init_lowlevel
>  #endif
> -	/*
> -	 * flush v4 I/D caches
> -	 */
> -	mov	r0, #0
> -	mcr	p15, 0, r0, c7, c7, 0	/* flush v3/v4 cache */
> -	mcr	p15, 0, r0, c8, c7, 0	/* flush v4 TLB */
> -
> -	/*
> -	 * disable MMU stuff and caches
> +#ifdef CONFIG_SOC_PRE_INIT
> +	/* Do SOC specific initalization here
> +	 * r0 contains the start address
> +	 * This allows for SOC code to configure
> +	 * based on current program execution context
> +	 * E.g.: NOR boot Vs SDRAM boot.
>  	 */
> -	mrc	p15, 0, r0, c1, c0, 0
> -	bic	r0, r0, #0x00002300	/* clear bits 13, 9:8 (--V- --RS) */
> -	bic	r0, r0, #0x00000087	/* clear bits 7, 2:0 (B--- -CAM) */
> -	orr	r0, r0, #0x00000002	/* set bit 2 (A) Align */
> -	orr	r0, r0, #0x00001000	/* set bit 12 (I) I-Cache */
> -	mcr	p15, 0, r0, c1, c0, 0
> +	mov r0,pc
> +	bl soc_init_crit
> +#endif	/* CONFIG_SOC_PRE_INIT */

We do not have any SoC specific init at the moment, but when you need it
lets introduce it here.

>  
>  	/*
> -	 * before relocating, we have to setup RAM timing
> -	 * because memory timing is board-dependend, you will
> -	 * find a lowlevel_init.S in your board directory.
> +	 * we do sys-critical inits only at reboot,
> +	 * not when booting from ram!
>  	 */
>  #ifndef CONFIG_SKIP_LOWLEVEL_INIT
> -	bl	board_init_lowlevel
> +	bl	cpu_init_crit
>  #endif
>  
> +#ifndef CONFIG_SKIP_RELOCATE_UBOOT
>  relocate:				/* relocate U-Boot to RAM	    */
>  	adr	r0, _start		/* r0 <- current position of code   */
>  	ldr	r1, _TEXT_BASE		/* test if we run from flash or RAM */
> @@ -176,6 +166,7 @@ copy_loop:
>  	stmia	r1!, {r3-r10}		/* copy to   target address [r1]    */
>  	cmp	r0, r2			/* until source end addreee [r2]    */
>  	ble	copy_loop
> +#endif	/* CONFIG_SKIP_RELOCATE_UBOOT */
>

No need to introduce this option. Look into the various board specific
lowlevel-init.S. They all check whether we run from RAM or not, so all
binaries can run from RAM or ROM without changes.
In case we run with start address == link address the relocation is
skipped anyway.

 
>  	/* Set up the stack						    */
>  stack_setup:
> @@ -199,6 +190,48 @@ clbss_l:str	r2, [r0]		/* clear loop...                    */
>  
>  _start_armboot:	.word start_uboot
>  
> +/*************************************************************************
> + *
> + * CPU_init_critical registers
> + *
> + * setup important registers
> + * setup memory timing
> + *
> + ************************************************************************/
> +#ifndef CONFIG_SKIP_LOWLEVEL_INIT
> +cpu_init_crit:
> +	/*
> +	 * flush v4 I/D caches
> +	 */
> +	mov	r0, #0
> +	mcr	p15, 0, r0, c7, c7, 0	/* flush v3/v4 cache */
> +	mcr	p15, 0, r0, c8, c7, 0	/* flush v4 TLB */
> +
> +	/*
> +	 * disable MMU stuff and caches
> +	 */
> +	mrc	p15, 0, r0, c1, c0, 0
> +	bic	r0, r0, #0x00002300	/* clear bits 13, 9:8 (--V- --RS) */
> +	bic	r0, r0, #0x00000087	/* clear bits 7, 2:0 (B--- -CAM) */
> +#ifdef CONFIG_ARM_ALIGN_ABRT
> +	orr	r0, r0, #0x00000002	/* set bit 2 (A) Align */
> +#endif
> +#ifdef CONFIG_ARM_I_CACHE
> +	orr	r0, r0, #0x00001000	/* set bit 12 (I) I-Cache */
> +#endif
> +	mcr	p15, 0, r0, c1, c0, 0
> +
> +	/*
> +	 * before relocating, we have to setup RAM timing
> +	 * because memory timing is board-dependent, you will
> +	 * find a lowlevel_init.S in your board directory.
> +	 */
> +	mov	ip, lr
> +	bl	board_init_lowlevel
> +	mov	lr, ip
> +	mov	pc, lr
> +#endif /* CONFIG_SKIP_LOWLEVEL_INIT */

Do we really need the SKIP_LOWLEVEL_INIT option? It should be safe to
run all times.

Sascha

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