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

[Masahiro Yamada]

Hi York,

2016-06-21 1:30 GMT+09:00 york sun <york.sun at nxp.com>:
> On 06/19/2016 03:34 AM, André Przywara wrote:
>> 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.
>>
>
> We have a team working on PSCI for ARMv8. The patches are floating and
> need some minor fix. With these patches, PSCI will be used instead of
> spin-table. However, a trusted firmware (or other kind) is required.
>


That's great.


So, what should we do about this patch?


I admit PSCI with ATF is the best way in the end,
but I believe having a simpler alternative should not hurt.




-- 
Best Regards
Masahiro Yamada