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From:   Anup Patel <anup@brainfault.org>
Date:   Thu, 26 Mar 2020 11:52:43 +0530
Message-ID: <CAAhSdy0+EYV3n3NPrJTkVZETm4SKrZLT1jLENJR9BAT5iGsCDw@mail.gmail.com>
Subject: Re: [RFC PATCH 3/7] riscv: Simplify MAXPHYSMEM config
To:     Alexandre Ghiti <alex@ghiti.fr>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Zong Li <zong.li@sifive.com>, Christoph Hellwig <hch@lst.de>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>
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On Sun, Mar 22, 2020 at 4:33 PM Alexandre Ghiti <alex@ghiti.fr> wrote:
>
> Either the user specifies maximum physical memory size of 2GB or the
> user lives with the system constraint which is 128GB in 64BIT for now.
>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
>  arch/riscv/Kconfig | 20 ++++++--------------
>  1 file changed, 6 insertions(+), 14 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 8e4b1cbcf2c2..a475c78e66bc 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -104,7 +104,7 @@ config PAGE_OFFSET
>         default 0xC0000000 if 32BIT && MAXPHYSMEM_2GB
>         default 0x80000000 if 64BIT && !MMU
>         default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB
> -       default 0xffffffe000000000 if 64BIT && MAXPHYSMEM_128GB
> +       default 0xffffffe000000000 if 64BIT && !MAXPHYSMEM_2GB
>
>  config ARCH_FLATMEM_ENABLE
>         def_bool y
> @@ -216,19 +216,11 @@ config MODULE_SECTIONS
>         bool
>         select HAVE_MOD_ARCH_SPECIFIC
>
> -choice
> -       prompt "Maximum Physical Memory"
> -       default MAXPHYSMEM_2GB if 32BIT
> -       default MAXPHYSMEM_2GB if 64BIT && CMODEL_MEDLOW
> -       default MAXPHYSMEM_128GB if 64BIT && CMODEL_MEDANY
> -
> -       config MAXPHYSMEM_2GB
> -               bool "2GiB"
> -       config MAXPHYSMEM_128GB
> -               depends on 64BIT && CMODEL_MEDANY
> -               bool "128GiB"
> -endchoice
> -
> +config MAXPHYSMEM_2GB
> +       bool "Maximum Physical Memory 2GiB"
> +       default y if 32BIT
> +       default y if 64BIT && CMODEL_MEDLOW
> +       default n
>
>  config SMP
>         bool "Symmetric Multi-Processing"
> --
> 2.20.1
>

Currently, we don't have systems with 256 GB or more memory
but I am sure quite a few organizations are working on server
class RISC-V.

Let's not force RV64 physical memory limit to 128GB by
removing MAXPHYSMEM_128GB. On the contrary, I suggest
to have more options such as MAXPHYSMEM_256GB,
MAXPHYSMEM_512GB, and MAXPHYSMEM_1TB.

Regards,
Anup