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SubjectRe: [Question] vendor-specific cpu enable-method

2018-09-13 11:29 GMT+09:00 Jisheng Zhang <>:
> On Thu, 13 Sep 2018 10:23:35 +0900 Masahiro Yamada wrote:
>> Hello.
>> Sorry if I am asking a stupid question.
>> For arm64, there are only 2 cpu methods, psci and spin-table.
>> Why do we still allow vendor-specific methods upstreamed
>> for arm 32bit ports?
>> To me, it looks like SoC vendors continue inventing
>> different (but similar) ways to do the same thing.
>> It is a historical reason for old platforms.
>> However, if I look at Documentation/devicetree/bindings/arm/cpus.txt
>> enable-method properties are still increasing.
>> psci is available in arch/arm/kernel/psci_smp.c,
>> but not all SoCs support the security extension.
>> Is there a simpler one like spin-table available for arm32?
> Per my understanding, spin-table is similar as the "pen" based
> solution in arm32, both can't reliably support kexec, suspend etc...

Right. spin-table is based on pen-based implementation,
and just a back-up plan in case psci is not available for some reasons.

>> If we force generic methods like psci or spin-table
>> for new platforms, we can stop proliferated smp code.
>> (Of course, we are just shifting the complexity
>> from the kernel to firmware.)
> psci is good but not all SoCs support secure extensions. spin-table
> can't support kexec, suspend. Except prefer psci for news SoCs
> with secure extensions, no better solutions AFAIK.

OK, psci is preferred if it is available.

Otherwise, ... vendor specific code.


Best Regards
Masahiro Yamada

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