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

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Date:   Tue, 7 Apr 2020 01:13:10 -0400
From:   Alex Ghiti <alex@...ti.fr>
To:     Palmer Dabbelt <palmer@...belt.com>
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
Subject: Re: [RFC PATCH 3/7] riscv: Simplify MAXPHYSMEM config


On 4/3/20 11:53 AM, Palmer Dabbelt wrote:
> 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.

With runtime sv48 introduction, whatever we would have used here could 
have been wrong at runtime, so removing it was easier.

Alex