linux-kernel - Re: [RFC PATCH 3/7] riscv: Simplify MAXPHYSMEM config

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Date:   Fri, 03 Apr 2020 08:53:11 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     alex@...ti.fr
CC:     Paul Walmsley <paul.walmsley@...ive.com>, zong.li@...ive.com,
        anup@...infault.org, Christoph Hellwig <hch@....de>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        alex@...ti.fr
Subject:     Re: [RFC PATCH 3/7] riscv: Simplify MAXPHYSMEM config

On Sun, 22 Mar 2020 04:00:24 PDT (-0700), alex@...ti.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@...ti.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"

I'm not sure this actually helps with anything, but if it's all going away then it's
fine.  Originally the 2G/128G stuff was there to allow for larger VA spaces in
the future.