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

>
> 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.

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