Re: [PATCH] ARM: Kconfig: improve ARM_SINGLE_ARMV7M description with Cortex M7

From: Vladimir Murzin <vladimir.murzin@arm.com>
To: Giulio Benetti <giulio.benetti@benettiengineering.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Cc: "Russell King" <linux@armlinux.org.uk>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>,
	"Ard Biesheuvel" <ardb@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Anshuman Khandual" <anshuman.khandual@arm.com>,
	"Geert Uytterhoeven" <geert+renesas@glider.be>,
	"Mike Rapoport" <rppt@kernel.org>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Lukas Bulwahn" <lukas.bulwahn@gmail.com>
Subject: Re: [PATCH] ARM: Kconfig: improve ARM_SINGLE_ARMV7M description with Cortex M7
Date: Fri, 3 Dec 2021 17:01:05 +0000	[thread overview]
Message-ID: <ea2679ec-9bfd-6a78-a82d-7b160350ddfb@arm.com> (raw)
In-Reply-To: <170aea55-44f3-9cf0-fd88-adf8c66efeb4@benettiengineering.com>

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

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