linux-kernel - Re: [PATCH 4/4] RISC-V: Fix maximum allowed phsyical memory for RV32

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Date:   Mon, 11 Jan 2021 09:34:07 +0530
From:   Anup Patel <anup@...infault.org>
To:     Atish Patra <atish.patra@....com>
Cc:     "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup.patel@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Nick Kossifidis <mick@....forth.gr>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mike Rapoport <rppt@...nel.org>
Subject: Re: [PATCH 4/4] RISC-V: Fix maximum allowed phsyical memory for RV32

On Thu, Jan 7, 2021 at 2:57 PM Atish Patra <atish.patra@....com> wrote:
>
> Linux kernel can only map 1GB of address space for RV32 as the page offset
> is set to 0xC0000000. The current description in the Kconfig is confusing
> as it indicates that RV32 can support 2GB of physical memory. That is
> simply not true for current kernel. In future, a 2GB split support can be
> added to allow 2GB physical address space.
>
> Signed-off-by: Atish Patra <atish.patra@....com>

Just for information, Alex's also has a patch to simplify this. Refer,
"[RFC PATCH 05/12] riscv: Simplify MAXPHYSMEM config"

Looks good to me.

Reviewed-by: Anup Patel <anup@...infault.org>

> ---
>  arch/riscv/Kconfig | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 81b76d44725d..e9e2c1f0a690 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -137,7 +137,7 @@ config PA_BITS
>
>  config PAGE_OFFSET
>         hex
> -       default 0xC0000000 if 32BIT && MAXPHYSMEM_2GB
> +       default 0xC0000000 if 32BIT && MAXPHYSMEM_1GB
>         default 0x80000000 if 64BIT && !MMU
>         default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB
>         default 0xffffffe000000000 if 64BIT && MAXPHYSMEM_128GB
> @@ -247,10 +247,12 @@ config MODULE_SECTIONS
>
>  choice
>         prompt "Maximum Physical Memory"
> -       default MAXPHYSMEM_2GB if 32BIT
> +       default MAXPHYSMEM_1GB if 32BIT
>         default MAXPHYSMEM_2GB if 64BIT && CMODEL_MEDLOW
>         default MAXPHYSMEM_128GB if 64BIT && CMODEL_MEDANY
>
> +       config MAXPHYSMEM_1GB
> +               bool "1GiB"
>         config MAXPHYSMEM_2GB
>                 bool "2GiB"
>         config MAXPHYSMEM_128GB
> --
> 2.25.1
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

Regards,
Anup

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