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

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Date:   Tue, 7 Sep 2021 21:27:46 +0900
From:   Daniel Palmer <daniel@...f.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Bert Vermeulen <bert@...t.com>,
        Russell King <linux@...linux.org.uk>,
        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

Hi Arnd,

On Tue, 7 Sept 2021 at 20:52, Arnd Bergmann <arnd@...db.de> wrote:
> > 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.

I wonder how fixable it would be..

I haven't gotten a board with the chip in question (SSD268G) yet but
from looking at some firmware binaries I can see that even u-boot is a
6 year old 32bit version.
As far as I can tell there's no PSCI, ATF etc that I think would be
expected for an arm64 machine.
I think the broken memory controller is still there so somehow I'd
need to get the heavy barrier to work in arm64. I haven't yet worked
out if that's even possible.
I think they are advertising that it supports up to 2GB of DDR. So
it's a hobbled 64bit capable system with highmem.

Putting most of the DT bits under arm64 even though it's so broken
it'll only ever boot a 32bit kernel makes sense to me.
Better than having lots of arm64 typical stuff like a newer GIC in a
file under arm and confusing everyone that comes across it.

Cheers,

Daniel