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

[Tom Warren]

Albert,

> -----Original Message-----
> From: Tom Warren [mailto:twarren.nvidia at gmail.com]
> Sent: Thursday, February 16, 2012 12:46 PM
> To: u-boot at lists.denx.de
> Cc: twarren.nvidia at gmail.com; albert.u.boot at aribaud.net; wd at denx.de;
> sjg at chromium.org; Stephen Warren; Tom Warren
> Subject: [PATCH] arm: Tegra2: Fix ELDK42 gcc failure with inline asm stack
> pointer load
> 
> 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));
> 
>  		start_cpu((u32)_start);
>  		halt_avp();
> --
> 1.7.7.1

This should fix the problem you had with compiling the 6 tegra2 builds w/ELDK42. I've also tested it with gcc 4.4.1 (the one I use every day) and gcc 4.6.1 (used internally @ NVIDIA for Chrome U-Boot builds, etc.). It's an ugly work-around, but it works. Thanks to Simon for the fix, BTW.
 
Tom

-- 
nvpublic