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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Mon, 9 Mar 2020 14:50:17 +0100
Message-ID: <CAK8P3a0Lc--pDmBG3mBiKyjpOEZVdKVBnLNYBdCjzdgN1byU3w@mail.gmail.com>
Subject: Re: [PATCH] soc: imx: Makefile: only build soc-imx8 when CONFIG_ARM64
To:     Peng Fan <peng.fan@nxp.com>
Cc:     Adam Ford <aford173@gmail.com>, Abel Vesa <abel.vesa@nxp.com>,
        Anson Huang <anson.huang@nxp.com>,
        "shawnguo@kernel.org" <shawnguo@kernel.org>,
        "s.hauer@pengutronix.de" <s.hauer@pengutronix.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        dl-linux-imx <linux-imx@nxp.com>,
        "kernel@pengutronix.de" <kernel@pengutronix.de>,
        =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>,
        Leonard Crestez <leonard.crestez@nxp.com>,
        "festevam@gmail.com" <festevam@gmail.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>
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On Mon, Mar 9, 2020 at 2:28 PM Peng Fan <peng.fan@nxp.com> wrote:
> > Subject: Re: [PATCH] soc: imx: Makefile: only build soc-imx8 when
> > CONFIG_ARM64
> >
> > On Mon, Jan 27, 2020 at 6:05 AM Peng Fan <peng.fan@nxp.com> wrote:
> > > > Subject: Re: [PATCH] soc: imx: Makefile: only build soc-imx8 when
> > > > Does anyone have any suggestions on where I might find some generic
> > > > stuff for either iMX8M or generic ARMv8 docs for doing something like
> > this?
> > >
> > > We did a porting for one customer, but code is not public available.
> > >
> > > First let uboot switch to AARCH32 mode when booting Linux, this is
> > > already supported by uboot mailine.
> > >
> > > Second, create a mach-imx8m.c under arch/arm/mach-imx to handle
> > i.MX8M
> > > just like other i.mx arm32 socs. This is not preferred by Linux community.
> > >
> > > 3rd, build i.MX8M drivers when using imx_v7_defconfig( or
> > > imx_v6_v7_defconfig in upstream)
> >
> > I think the third part is something we can clearly do once it actually boots.
> >
> > Can you post the patch for the second part for reference? In theory nothing
> > should be necessary there, so I wonder what I'm missing (as we need no code
> > for arch/arm64) and what we can do differently to make it work out of the
> > box.
> >
> > Is the problem that the SMP bringup using PSCI for arm64 doesn't work with
> > the 32-bit kernel for some reason?
>
> Sorry for long time delay. I forgot your mail. I did some try again, seems only need
> the following piece code to make it boot, also select GIC_V3 and drop some ARM64
> dependencies in Kconfig for some i.MX drivers.
> Need some addition work in ATF/U-Boot
> to make smp work, that is not Linux related.

Ah, nice!

> +static const char *const imx8mm_dt_compat[] __initconst = {
> +       "fsl,imx8mm",
> +       NULL,
> +};
> +
> +#include <asm/mach/arch.h>
> +DT_MACHINE_START(IMX7D, "Freescale i.MX8MM (Device Tree)")
> +       .dt_compat      = imx8mm_dt_compat,
> +MACHINE_END
>
>
> Are you ok we add such piece code in drivers/soc/imx/soc-imx8.c to support
> aarch32 linux?

I don't think that code does anything other than set the machine name. Are you
sure it doesn't work without that?

If it's indeed required, I'd prefer to add a file for in arch/arm/mach-imx than
in drivers/soc/.

      Arnd