* [U-Boot-Users] Uboot-V2: ARM: towards a common start-arm.S
2008-03-17 22:32 [U-Boot-Users] Uboot-V2: ARM: towards a common start-arm.S Nishanth Menon
@ 2008-03-18 12:19 ` Sascha Hauer
0 siblings, 0 replies; 2+ messages in thread
From: Sascha Hauer @ 2008-03-18 12:19 UTC (permalink / raw)
To: u-boot
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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