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

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Date:   Tue, 17 Mar 2020 01:44:30 +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
> 
> 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.

Tested with imx_v6_v7_defconfig without LPAE, smp boots up with nfsroot.

Thanks,
Peng.

> 
> 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