[U-Boot] tegra20: add back USE_PRIVATE_LIBGCC

On Tue, Aug 07, 2012 at 10:53:00AM -0700, Lucas Stach wrote:
> Hi Allen,
> 
> And to answer Tom's question: the failure was that the real U-Boot would
> not come up after the SPL. All I could see was the one line printed by
> the SPL and nothing more.

I think I found the problem.  It's the following code from start.S:

ENTRY(cpu_init_crit)
       /*
        * Jump to board specific initialization...
        * The Mask ROM will have already initialized
        * basic memory. Go here to bump up clock rate and handle
        * wake up conditions.
        */
       mov     ip, lr                  @ persevere link reg across
       call
       bl      lowlevel_init           @ go setup pll,mux,memory
       mov     lr, ip                  @ restore link
       mov     pc, lr                  @ back to my caller
ENDPROC(cpu_init_crit)


The "ip" register is not preserved across function calls, and the
CodeSourcery compiler is using it in lowlevel_init or one of the
functions it calls.  This code was there before the SPL changes, but
wasn't being called because CONFIG_SKIP_LOWLEVEL_INIT was set, but now
it isn't.

Lucas, can you try the following change?  I tested it on seaboard with
CodeSourcery arm-2011.09-70-arm-none-linux-gnueabi and I'm able to
boot a kernel.

Tom if this works we probably want to get it into your pull request to
Albert.  CodeSourcery toolchain is probably used by a lot of people.

-Allen

Am Dienstag, den 07.08.2012, 15:28 -0700 schrieb Allen Martin:
> On Tue, Aug 07, 2012 at 10:53:00AM -0700, Lucas Stach wrote:
> > Hi Allen,
> > 
> > And to answer Tom's question: the failure was that the real U-Boot would
> > not come up after the SPL. All I could see was the one line printed by
> > the SPL and nothing more.
> 
> I think I found the problem.  It's the following code from start.S:
> 
> ENTRY(cpu_init_crit)
>        /*
>         * Jump to board specific initialization...
>         * The Mask ROM will have already initialized
>         * basic memory. Go here to bump up clock rate and handle
>         * wake up conditions.
>         */
>        mov     ip, lr                  @ persevere link reg across
>        call
>        bl      lowlevel_init           @ go setup pll,mux,memory
>        mov     lr, ip                  @ restore link
>        mov     pc, lr                  @ back to my caller
> ENDPROC(cpu_init_crit)
> 
> 
> The "ip" register is not preserved across function calls, and the
> CodeSourcery compiler is using it in lowlevel_init or one of the
> functions it calls.  This code was there before the SPL changes, but
> wasn't being called because CONFIG_SKIP_LOWLEVEL_INIT was set, but now
> it isn't.
> 
> Lucas, can you try the following change?  I tested it on seaboard with
> CodeSourcery arm-2011.09-70-arm-none-linux-gnueabi and I'm able to
> boot a kernel.

Yes I can confirm this fixes the issue without further workarounds.
Thanks, and:

Tested-by: Lucas Stach <dev@lynxeye.de>
> 
> Tom if this works we probably want to get it into your pull request to
> Albert.  CodeSourcery toolchain is probably used by a lot of people.
> 
> -Allen
> 
> 
> diff --git a/arch/arm/cpu/armv7/start.S b/arch/arm/cpu/armv7/start.S
> index 2506f27..02e47fa 100644
> --- a/arch/arm/cpu/armv7/start.S
> +++ b/arch/arm/cpu/armv7/start.S
> @@ -152,7 +152,7 @@ reset:
>         /* the mask ROM code should have PLL and others stable */
>  #ifndef CONFIG_SKIP_LOWLEVEL_INIT
>         bl      cpu_init_cp15
> -       bl      cpu_init_crit
> +       bl      lowlevel_init           @ go setup pll,mux,memory
>  #endif
> 
>  /* Set stackpointer in internal RAM to call board_init_f */
> @@ -339,29 +339,6 @@ ENTRY(cpu_init_cp15)
>         mov     pc, lr                  @ back to my caller
>  ENDPROC(cpu_init_cp15)
> 
> -#ifndef CONFIG_SKIP_LOWLEVEL_INIT
> -/*************************************************************************
> - *
> - * CPU_init_critical registers
> - *
> - * setup important registers
> - * setup memory timing
> - *
> - *************************************************************************/
> -ENTRY(cpu_init_crit)
> -       /*
> -        * Jump to board specific initialization...
> -        * The Mask ROM will have already initialized
> -        * basic memory. Go here to bump up clock rate and handle
> -        * wake up conditions.
> -        */
> -       mov     ip, lr                  @ persevere link reg across
> -call
> -       bl      lowlevel_init           @ go setup pll,mux,memory
> -       mov     lr, ip                  @ restore link
> -       mov     pc, lr                  @ back to my caller
> -ENDPROC(cpu_init_crit)
> -#endif
> -
>  #ifndef CONFIG_SPL_BUILD
>  /*
>   *************************************************************************
> 
>

On Tue, Aug 07, 2012 at 03:42:45PM -0700, Lucas Stach wrote:
> Am Dienstag, den 07.08.2012, 15:28 -0700 schrieb Allen Martin:
> > On Tue, Aug 07, 2012 at 10:53:00AM -0700, Lucas Stach wrote:
> > > Hi Allen,
> > > 
> > > And to answer Tom's question: the failure was that the real U-Boot would
> > > not come up after the SPL. All I could see was the one line printed by
> > > the SPL and nothing more.
> > 
> > I think I found the problem.  It's the following code from start.S:
> > 
> > ENTRY(cpu_init_crit)
> >        /*
> >         * Jump to board specific initialization...
> >         * The Mask ROM will have already initialized
> >         * basic memory. Go here to bump up clock rate and handle
> >         * wake up conditions.
> >         */
> >        mov     ip, lr                  @ persevere link reg across
> >        call
> >        bl      lowlevel_init           @ go setup pll,mux,memory
> >        mov     lr, ip                  @ restore link
> >        mov     pc, lr                  @ back to my caller
> > ENDPROC(cpu_init_crit)
> > 
> > 
> > The "ip" register is not preserved across function calls, and the
> > CodeSourcery compiler is using it in lowlevel_init or one of the
> > functions it calls.  This code was there before the SPL changes, but
> > wasn't being called because CONFIG_SKIP_LOWLEVEL_INIT was set, but now
> > it isn't.
> > 
> > Lucas, can you try the following change?  I tested it on seaboard with
> > CodeSourcery arm-2011.09-70-arm-none-linux-gnueabi and I'm able to
> > boot a kernel.
> 
> Yes I can confirm this fixes the issue without further workarounds.
> Thanks, and:
> 
> Tested-by: Lucas Stach <dev@lynxeye.de>

Digging a little deeper into this, cpu_init_crit() and lowlevel_init()
are called before the stack is setup, so the fact that we call into C
code on tegra here is probably the bigger issue.  I think the correct
fix here is for me to move the code from lowlevel_init() to
board_init_f(). 

-Allen