linux-kernel - Re: [PATCH 1/6] MIPS: Loongson64: Do not write the read only field LPA of CP0

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Date:   Fri, 30 Oct 2020 20:13:09 +0800
From:   Jiaxun Yang <jiaxun.yang@...goat.com>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Huacai Chen <chenhc@...ote.com>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>
Subject: Re: [PATCH 1/6] MIPS: Loongson64: Do not write the read only field
 LPA of CP0_CONFIG3



在 2020/10/30 14:22, Tiezhu Yang 写道:
> On 10/30/2020 12:00 PM, Jiaxun Yang wrote:
>>
>>
>> 在 2020/10/29 16:02, Tiezhu Yang 写道:
>>> The field LPA of CP0_CONFIG3 register is read only for Loongson64, 
>>> so the
>>> write operations are meaningless, remove them.
>>>
>>> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
>>> ---
>>>   arch/mips/include/asm/mach-loongson64/kernel-entry-init.h | 8 
>>> --------
>>>   arch/mips/loongson64/numa.c                               | 3 ---
>>>   2 files changed, 11 deletions(-)
>> Hi Tiezhu,
>>
>> AFAIK it's not read only on 3A1000.
>> Have you check with hardware guys?
>
> Hi Jiaxun,
>
> Yes, I checked it before send this patch,  the field LPA of CP0_CONFIG3
> on 3A1000 is also read only,  we can see the related description in the
> chapter 3.22 of Loongson_3A1000_cpu_user_2.

On page 36, it said:
"能否写ELPA位依赖于Config3寄存器的LPA域 。当Config3的LPA位为0时，
PageGrain的ELPA位被置位。"

Don't know if it matters.

@Huacai, Any comments? Do you know why it exists here?

Thanks

- Jiaxun