linux-kernel - Re: [Question] vendor-specific cpu enable-method

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Date:   Fri, 14 Sep 2018 17:37:35 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Olof Johansson <olof@...om.net>,
        Rob Herring <robh+dt@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Question] vendor-specific cpu enable-method

Hi.


2018-09-13 11:29 GMT+09:00 Jisheng Zhang <Jisheng.Zhang@...aptics.com>:
> 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.


Thanks.


-- 
Best Regards
Masahiro Yamada