linux-kernel - Re: [PATCH v2 4/5] ARM: Add basic support for Airoha EN7523 SoC

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Date:   Tue, 7 Sep 2021 13:51:59 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Daniel Palmer <daniel@...f.com>
Cc:     Bert Vermeulen <bert@...t.com>,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        John Crispin <john@...ozen.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        YiFei Zhu <yifeifz2@...inois.edu>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Mike Rapoport <rppt@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 4/5] ARM: Add basic support for Airoha EN7523 SoC

On Tue, Sep 7, 2021 at 12:48 PM Daniel Palmer <daniel@...f.com> wrote:
> On Tue, 7 Sept 2021 at 19:30, Bert Vermeulen <bert@...t.com> wrote:
> >
> > From: John Crispin <john@...ozen.org>
> >
> > EN7523 is an armv7 based silicon used inside broadband access type devices
> > such as xPON and xDSL. It shares various silicon blocks with MediaTek
> > silicon such as the MT7622.
>
> This is a Cortex A53 isn't it? So it's ARMv8. I thought the issue is
> that it's actually a 64bit system but you only have a 32bit
> bootloader, firmware etc?
>
> Off-topic but related:  Another MediaTek spin off, SigmaStar, seems to
> have done exactly the same thing. Cortex A53 chip running as a 32bit
> system to avoid having to fix their software. I'm interested to see if
> this makes it into arm or arm64. :)

Maybe it's best to just add them to both at the same time? The boot
loader situation might take a bit to work out, but in theory this should
be fixable.

You can generally include .dtsi files from one in the other, as you can
see from e.g. arch/arm64/boot/dts/broadcom/bcm2837-rpi-3-b.dts.

For new files, I think I would prefer having the .dts files in arm64 and
including them from arch/arm/ rather than the other way round, but
others may come up with a good reason to keep doing the reverse.
This would help encourage the thought that running a 64-bit
kernel is the better setup, rather than propagate the 32-bit kernel
nonsense on 64-bit machines.

       Arnd