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From:   Alistair Francis <alistair23@gmail.com>
Date:   Wed, 3 Feb 2021 22:55:58 -0800
Message-ID: <CAKmqyKPukAOA5rw2c6cjGKmoTo5HFudtwS4_6P7DGCiGGHGbgA@mail.gmail.com>
Subject: Re: [PATCH v2 3/3] arch/arm/configs: Enable VMSPLIT_2G in imx_v6_v7_defconfig
To:     Arnd Bergmann <arnd@kernel.org>
Cc:     Shawn Guo <shawnguo@kernel.org>,
        Alistair Francis <alistair@alistair23.me>,
        Arnd Bergmann <arnd@arndb.de>, Olof Johansson <olof@lixom.net>,
        Rob Herring <robh+dt@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Sascha Hauer <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>,
        dl-linux-imx <linux-imx@nxp.com>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        devicetree <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Tue, Feb 2, 2021 at 11:50 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> On Wed, Feb 3, 2021 at 3:37 AM Alistair Francis <alistair23@gmail.com> wrote:
> >
> > On Thu, Jan 28, 2021 at 11:13 PM Shawn Guo <shawnguo@kernel.org> wrote:
> > >
> > > On Sun, Jan 17, 2021 at 10:03:01AM -0800, Alistair Francis wrote:
> > > > The reMarkable2 requires VMSPLIT_2G, so lets set this in the
> > > > imx_v6_v7_defconfig.
> > >
> > > Hmm, why is VMSPLIT_2G required by reMarkable2?
> >
> > I'm not too sure. It's difficult to debug problems as I only have a
> > UART but without this I don't see any kernel prints so it seems like
> > the kernel doesn't get very far. I haven't had any luck with earlycon
> > on the device so I don't know how I can get more information.
>
> In the dts file, I can see that the machine has 1GB of RAM at
> contiguous addresses. My first guess would be a problem with
> highmem, as this configuration means that with VMSPLIT_3G
> there are 768MB of lowmem and 256MB of highmem.
>
> Can you try these two things to narrow the problem down
> further?
>
> a) disable CONFIG_HIGHMEM when using VMSPLIT_3G
> b) use VMSPLIT_3G_OPT

Thanks Arnd,

I was working on testing the config changes you mentioned, but it
seems like all of them work now.

VMSPLIT_2G: Boots to userspace

VMSPLIT_3G && HIGHMEM: Boots to userspace

VMSPLIT_3G && !HIGHMEM: Boots to userspace

VMSPLIT_3G_OPT && HIGHMEM:Boots to userspace

>
> If both of them solve the problem, then highmem is likely
> the root cause. One possible issue might be that the boot
> loader loads the initramfs or the dtb into a location outside
> of the first 768 MB of lowmem where it is unreachable
> in the VMSPLIT_3G configuration.

It boots with u-boot, which I am building so I can change these addresses.

I'm guessing that I have changed the addresses at some point and now
it works. I'm going to drop this patch.

Alistair

>
>         Arnd