[U-Boot] [PATCH 2/2] arm64: add better spin-table support

[André Przywara]

Hi,

On 19/06/16 09:57, Masahiro Yamada wrote:
> 2016-06-18 18:40 GMT+09:00 Linus Walleij <linus.walleij at linaro.org>:
>> On Fri, Jun 17, 2016 at 2:51 PM, Masahiro Yamada
>> <yamada.masahiro at socionext.com> wrote:
>>
>>> There are two enable methods supported by ARM64 Linux; psci and
>>> spin-table.  The latter is simpler and easier to use for quick SoC
>>> bring-up.
>>>
>>> So, I used the spin-table for my first ARMv8 SoC porting, but I
>>> found its support in U-Boot was poor.  It is true there exists a
>>> code fragment for the spin code in arch/arm/cpu/armv8/start.S,
>>> but I see some problems:
>>
>> Is part of the motivation for this approach to boot an ARMv8 system
>> without using the ARM Trusted Firmware?
>>
>> Yours,
>> Linus Walleij
> 
> Yes, exactly.
> 
> It would be the best choice
> to switch over to PSCI with ATF in a long run,
> but, I decided to use spin-table for the initial SoC bring-up
> because of tight schedule.

So if you don't have an ATF port ready, why not use U-Boot's PSCI
implementation meanwhile? I think there are efforts underway to make
PSCI enablement for random new boards a walk in the park (by making the
PSCI support as generic as possible, CCing Chen-Yu for this).

IIRC the spin-table boot method was just introduced to cope with cores
that don't have EL3 and thus cannot provide PSCI services the normal way
(and that don't want to or cannot sacrifice EL2 for that).
So I am a bit wary of proliferating this SMP method.

Wouldn't it be better to help making U-Boot's PSCI stack as easy to use
as possible? I don't see technical reasons that adding PSCI support for
a board should be harder or more involved than adding spin-table support
- in the end you need to tell it about the SMP pen, maybe providing (or
faking?) reset and shutdown for 0.2 compliance.

Cheers,
Andre.

> If I use spin-table, I can keep the boot sequence very simple.