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

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Date:   Fri, 3 Dec 2021 18:03:34 +0100
From:   Giulio Benetti <giulio.benetti@...ettiengineering.com>
To:     Vladimir Murzin <vladimir.murzin@....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 03/12/21 18:01, Vladimir Murzin wrote:
> 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].

Ah, I've missed that. And great for M33!

>> 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)

Ah yeah, thanks for pointing, then I'm going with ARMv7-M/v8-M

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

+1

Thank you
Best regards
-- 
Giulio Benetti
Benetti Engineering sas

> [1] https://lore.kernel.org/linux-arm-kernel/20211201132908.106711-1-vladimir.murzin@arm.com/T/
> 
> Cheers
> Vladimir
> 
>>
>> Best regards
>