[U-Boot] [PATCH] arm: Tegra2: add support for A9 CPU init

[Tom Warren]

Allesandro,

On Thu, Mar 17, 2011 at 8:30 AM, Alessandro Rubini
<rubini-list at gnudd.com> wrote:
>
>>> It looks like most of your uses are standalone functions that would
>>> function just fine on their own.  Is there a reason you prefer to have
>>> them in a C-file instead of in an assembly file?
>
>> Just laziness ;)
>> I'll move these to a new .S file in the next patchset.
>
> Actually, writing assembly-only C functions is difficul and
> error-pronet. I've seen you use "r0" and other registers esplicitly,
> but this is not allowed in general.
>
> I once wasted some hours in tracking why a non-submitted port of
> u-boot was not working with a newer compiler. The problem was just
> that: the new compiler was inlining a void(void) function; the asm
> used "r0" and "r1" explicitly, which worked over a function call
> but was corrupting data when inlined by the newer and more optimizing
> compiler.
I've moved most of the in-line assembly to lowlevel_init.S.
However, the cold_boot() code proved difficult - I got fixup errors,
undefined constants, etc.
I've cleaned it up a bit, but left it in ap20.c, using the %vars -
again, replacing them with the actual values caused errors that I
couldn't resolve.
Maybe someone else on the list can help to port this code to the
assembly file - I'm not expert enough in gcc/as and ARM to do it.
New patch to follow RSN.

>
> While your functions are currently not inlined (or, like cold_boot,
> they may be inlined in a place where no register needs to be
> preserved), another user may move them to a context where the
> semantics are different, for another board or another boot loader.  If
> they are in a .S files, they will only be called by "bl" and you know
> the rules for register allocation appy. Besides, a _real_ lazy
> programmer avoids the extra quotes and \n in the code :)
>
> /alessandro
Thanks for your insight,
Tom
>