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

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Date:   Mon, 2 Nov 2020 18:47:50 +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 20:13, Jiaxun Yang 写道:
>
>
> 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?

Confirmed by another rev of the manual that it's only a tip for implementer.
I guess my assumption was wrong.
LPA should be read-only though.....

Thanks
- Jiaxun

>
> Thanks
>
> - Jiaxun