[U-Boot] [PATCH] arm: Tegra2: Fix ELDK42 gcc failure with inline asm stack pointer load

[Marek Vasut]

> The 4.2.2 gcc in the ELDK42 release doesn't like the direct SP
> load using a constant in tegra2_start. Break it up into 4 loads
> using mov & orr.
> 
> Tested on my Seaboard T20-A03, U-Boot loads and runs OK. Also
> compiled all tegra2 builds with both gcc 4.2.2 and 4.4.1 OK.
> 
> Signed-off-by: Tom Warren <twarren at nvidia.com>
> ---
>  arch/arm/cpu/armv7/tegra2/ap20.c |   25 ++++++++++++++++++++-----
>  1 files changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm/cpu/armv7/tegra2/ap20.c
> b/arch/arm/cpu/armv7/tegra2/ap20.c index 4c44bb3..d2bc0d5 100644
> --- a/arch/arm/cpu/armv7/tegra2/ap20.c
> +++ b/arch/arm/cpu/armv7/tegra2/ap20.c
> @@ -298,11 +298,26 @@ void tegra2_start(void)
>  		writel(0xC0, &pmt->pmt_cfg_ctl);
> 
>  		/*
> -		* If we are ARM7 - give it a different stack. We are about to
> -		* start up the A9 which will want to use this one.
> -		*/
> -		asm volatile("ldr	sp, =%c0\n"
> -			: : "i"(AVP_EARLY_BOOT_STACK_LIMIT));
> +		 * If we are ARM7 - give it a different stack. We are about to
> +		 * start up the A9 which will want to use this one.
> +		 */
> +		/*
> +		 * Note that the 'ldr sp,CONSTANT' version, below, doesn't
> +		 * work on gcc 4.2.2 (ELDK42), but does on gcc 4.4.1 and above.
> +		 * The work-around is to use the (ugly) 4-pass mov/orr below.
> +		 *
> +		 * asm volatile("ldr	sp, =%c0\n" : :
> +		 *	"i"(AVP_EARLY_BOOT_STACK_LIMIT));
> +		 */
> +
> +		asm volatile("mov	sp, %0"
> +			: : "i"(AVP_EARLY_BOOT_STACK_LIMIT & 0xFF));
> +		asm volatile("orr	sp, %0"
> +			: : "i"(AVP_EARLY_BOOT_STACK_LIMIT & 0xFF00));
> +		asm volatile("orr	sp, %0"
> +			: : "i"(AVP_EARLY_BOOT_STACK_LIMIT & 0xFF0000));
> +		asm volatile("orr	sp, %0"
> +			: : "i"(AVP_EARLY_BOOT_STACK_LIMIT & 0xFF000000));

asm volatile("mov sp, %0"::"r"(AVP_EARLY_BOOT_STACK_LIMIT)); won't work?

M
> 
>  		start_cpu((u32)_start);
>  		halt_avp();