linux-kernel - Re: [PATCH] ARM: Kconfig: improve ARM_SINGLE

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Message-ID: <ea2679ec-9bfd-6a78-a82d-7b160350ddfb@arm.com>
Date:   Fri, 3 Dec 2021 17:01:05 +0000
From:   Vladimir Murzin <vladimir.murzin@....com>
To:     Giulio Benetti <giulio.benetti@...ettiengineering.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Mike Rapoport <rppt@...nel.org>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>
Subject: Re: [PATCH] ARM: Kconfig: improve ARM_SINGLE_ARMV7M description with
 Cortex M7

On 12/3/21 4:41 PM, Giulio Benetti wrote:
> Hi Vladimir,
> 
> On 03/12/21 10:30, Vladimir Murzin wrote:
>> On 12/2/21 10:20 PM, Giulio Benetti wrote:
>>> ARM_SINGLE_ARMV7M implies Arm Cortex M7 too, so let's add it to
>>> description with M0/M3/M4.
>>
>> Well it also implies M33 and M55. I'd suggest drop specific implementations
>> from description - so we do not need to update it each time new compatible
>> core is released. To account newest cores like M33 and M55 you can rephrase
>> to:
>> - ARMv7-M/v8-M
> 
> This ^^^ is ok for me. Also, I don't see any M0 used at the moment so no ARMv6-M makes sense, if any in the future we can update. I see M3,M4,M7 for the moment, so ARMv7-M. But at the moment no ARMv8-M, or am I wrong?

We already support PMSAv8 which is ARMv8-M, M33/M55 is in flight [1].

> Maybe it would be better to add ARMv8-M when there will really be the support, considering also that ARM_SINGLE_ARMV7M is a bit ambiguous to be used with ARMv8-M. So maybe that could be modified too when an ARMv8-M is added.
> 
> What do you think about this?

Well, I prefer to touch this as rare as possible, and if we touch
it then ensure we do not need to touch it for a long time ;)

Look at A-class cores, 

config ARCH_MULTI_V7
        bool "ARMv7 based platforms (Cortex-A, PJ4, Scorpion, Krait)"

it doesn't mention ARMv8, yet it is pretty much possible to run it
on some cores either bare-metal or as a guest (just look under
arch/arm/include/asm/cputype.h)

These are just config options, not a legal deeds...

[1] https://lore.kernel.org/linux-arm-kernel/20211201132908.106711-1-vladimir.murzin@arm.com/T/

Cheers
Vladimir

> 
> Best regards