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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Fri, 13 Mar 2020 19:47:44 +0900
Message-ID: <CAK7LNASfQmpVxG7N9_ZL4uTaMY2DeP-Y1aAdP72eatD936zkYA@mail.gmail.com>
Subject: Re: [PATCH] ARM: dts: Makefile: build arm64 device tree
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Peng Fan <peng.fan@nxp.com>, Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Shawn Guo <shawnguo@kernel.org>,
        DTML <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        NXP Linux Team <linux-imx@nxp.com>
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On Fri, Mar 13, 2020 at 7:23 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Fri, Mar 13, 2020 at 4:38 AM <peng.fan@nxp.com> wrote:
> >
> > From: Peng Fan <peng.fan@nxp.com>
> >
> > To support aarch32 mode linux on aarch64 hardware, we need
> > build the device tree, so include the arm64 device tree path.
> >
> > Signed-off-by: Peng Fan <peng.fan@nxp.com>
> > ---
>
> There are a few other platforms with similar requirements, in
> particular bcm2837,
> so maybe try doing it the same way they do, see
> arch/arm64/boot/dts/broadcom/bcm2837-rpi-3-b.dts

I think this was discussed over again,
but it is odd to tightly couple
DT and Linux arch.


Maybe, a long time solution might be to
create a new directory, dts/
and collect all DT stuff into it.

dts/<vendor>/<board>.dts


Then, also move like follows:

Documentation/devicetree/bindings/
 ->  dts/Bindings/

include/dt-bingins/
 -> dts/include/dt-bindings/


>
> > V1:
> >  This is just the device tree part. Besides this,
> >  I am not sure whether need to create a standalone defconfig under arm32
> >  for aarch32 mode linux on aarch64 hardware, or use multi_v7_defconfig.
> >  multi_v7_defconfig should be ok, need to include LPAE config.
>
> I'd rather not have a standalone defconfig for it, given that we have a
> single defconfig for all armv6/armv7/armv7hf i.mx machines.
>
> There was a suggestion to use a fragment for enabling an LPAE
> multi_v7_defconfig recently, which I think is still under discussion but
> should also help here, both with imx_v6_v7_defconfig and multi_v7_defconfig.
>
> Can you remind us why this platform needs LPAE? Is it only needed to
> support more than 4GB of RAM, or something else on top of that?
> Note that users that actually have 4GB or more on i.mx8 should
> really run a 64-bit kernel anyway, even if they prefer using 32-bit user
> space.
>
> Turning on LPAE not only disables imx3 and imx5 but also the Cortex-A9
> based imx6 variants.
>
>       Arnd


-- 
Best Regards
Masahiro Yamada