linux-kernel - RE: [PATCH] ARM: dts: Makefile: build arm64 device tree

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Message-ID: <AM0PR04MB4481CD81915F8A9FB115A97788FA0@AM0PR04MB4481.eurprd04.prod.outlook.com>
Date:   Fri, 13 Mar 2020 12:39:03 +0000
From:   Peng Fan <peng.fan@....com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        DTML <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH] ARM: dts: Makefile: build arm64 device tree

Hi Arnd,

> Subject: Re: [PATCH] ARM: dts: Makefile: build arm64 device tree
> 
> On Fri, Mar 13, 2020 at 4:38 AM <peng.fan@....com> wrote:
> >
> > From: Peng Fan <peng.fan@....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@....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
> 
> > 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?

Currently I only tested LPAE enabled arm32 kernel, I'll give a try with LPAE
disabled later.

Thanks,
Peng.
> 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