[U-Boot] [PATCH 2/5] ARM: arm926ejs: fix lowlevel_init call

[Chris Packham]

Hi Mans, Stefano,

On Fri, Apr 27, 2018 at 9:00 PM Stefano Babic <sbabic at denx.de> wrote:

> On 21/04/2018 17:11, Mans Rullgard wrote:
> > The code attempts to preserve the value of LR by storing it in R12/IP
> > across the lowevel_init() call.  However, this register is not saved
> > by the callee.  Use a register that guaranteed to be preserved instead.
> >
> > Signed-off-by: Mans Rullgard <mans at mansr.com>
> > ---
> >  arch/arm/cpu/arm926ejs/start.S | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm/cpu/arm926ejs/start.S
b/arch/arm/cpu/arm926ejs/start.S
> > index 959d1ed86d8a..a6f0bdb70345 100644
> > --- a/arch/arm/cpu/arm926ejs/start.S
> > +++ b/arch/arm/cpu/arm926ejs/start.S
> > @@ -105,9 +105,9 @@ flush_dcache:
> >       /*
> >        * Go setup Memory and board specific bits prior to relocation.
> >        */
> > -     mov     ip, lr          /* perserve link reg across call */
> > +     mov     r4, lr          /* perserve link reg across call */
> >       bl      lowlevel_init   /* go setup pll,mux,memory */
> > -     mov     lr, ip          /* restore link */
> > +     mov     lr, r4          /* restore link */
> >  #endif
> >       mov     pc, lr          /* back to my caller */
> >  #endif /* CONFIG_SKIP_LOWLEVEL_INIT */
> >

> Applied to u-boot-imx, thanks !

I think this might be causing me a problem on a Marvell Kirkwood board I'm
working on getting into upstream. It may also be problematic for orion5x
boards. Both of these use r4 in lowlevel_init.

Obviously I can fix the board that I'm working on. Is there some
expectation as to which registers can be clobbered?