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

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Date:   Thu, 13 Sep 2018 10:29:46 +0800
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.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

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.