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

[Tom Warren]

Marek,

> -----Original Message-----
> From: Marek Vasut [mailto:marek.vasut at gmail.com]
> Sent: Thursday, February 16, 2012 3:47 PM
> To: u-boot at lists.denx.de
> Cc: Tom Warren; Tom Warren
> Subject: Re: [U-Boot] [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));
> 
> asm volatile("mov sp, %0"::"r"(AVP_EARLY_BOOT_STACK_LIMIT)); won't work?

That actually _did_ work. I'd thought I'd tried all iterations of ldr/mov/etc., including some that compiled OK but gave fixup errors in the linker, but I guess I missed that one.

Thanks. I'll retest and resubmit.

Tom
> 
> M
> >
> >  		start_cpu((u32)_start);
> >  		halt_avp();
-- 
nvpublic