[U-Boot] [PATCH 3/5] arm: Allow lr to be saved by board code

[Simon Glass]

Hi Albert,

On 5 February 2015 at 07:15, Albert ARIBAUD <albert.u.boot at aribaud.net> wrote:
> Hello Simon,
>
> On Wed, 4 Feb 2015 19:51:36 -0700, Simon Glass <sjg at chromium.org> wrote:
>> Hi Albert,
>>
>> On 4 February 2015 at 01:59, Albert ARIBAUD <albert.u.boot at aribaud.net> wrote:
>> > Hello Simon,
>> >
>> > On Tue,  3 Feb 2015 21:18:52 -0700, Simon Glass <sjg at chromium.org>
>> > wrote:
>> >> The link register value can be required on some boards (e.g. FEL mode on
>> >> sunxi) so stash it to r4 before jumping to save_boot_params().
>> >
>> > I'd rather not make this there; I would like save_boot_params to start
>> > with as unmodified a core state as possible, because r4 might
>> > actually, now or in the future, contain important data.
>> >
>> > I'd even go as far as saying that save_boot_params should be branched
>> > into rather than called, and should branch back to a fixed label right
>> > after reset, so that even lr is preserved. For SoCs which do not need
>> > to save any boot parameters, a weak version of save_boot_params would
>> > just do the branching back.
>> >
>> > (this should help merging all start.S instances into a singe one,
>> > which I still want to achieve one day)
>>
>> I did consider this but was worried that some save_boot_params()
>> functions are written in C (OMAP) so this would not work. But if we
>> can require it to be written in assembler, or provide an asm macro to
>> return from the C function, then I can do that. What do you think?
>
> I think that save_boot_params runs right at reset and cannot rely on any
> C environment at all, and should indeed be written in asm and only deal
> with *very urgent* savings; only those registers that would be lost
> almost immediately, like r0-r14 and some system registers. Anything
> else is less urgent and can be processed later, possibly even in
> board_init_f().
>
> That being said, OMAP does not have save_boot_params in C that I can
> find; actualy, doing a 'git grep save_boot_param -- *.c' shows only
> one occurrence, in arch/arm/cpu/armv7/exynos/spl_boot.c, ar line 312,
> and it's an empty function. OMAP has an s_init C implementation,
> though.

Ah yes, I may have been thinking of exynos and since it is empty it
can be dropped. I'll go ahead and change this and resend once we have
the other issues resolved.

Regards,
Simon