Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
AI-Spam-Status: Not processed
Subject: Re: [PATCH 1/6] MIPS: Loongson64: Do not write the read only field
 LPA of CP0_CONFIG3
From:   Jiaxun Yang <jiaxun.yang@flygoat.com>
To:     Tiezhu Yang <yangtiezhu@loongson.cn>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Huacai Chen <chenhc@lemote.com>
Cc:     linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
        Xuefeng Li <lixuefeng@loongson.cn>
References: <1603958581-4723-1-git-send-email-yangtiezhu@loongson.cn>
 <1603958581-4723-2-git-send-email-yangtiezhu@loongson.cn>
 <a384c467-048d-1296-4a0d-ecbf4cea844d@flygoat.com>
 <7306f77f-b70a-862d-b4c5-d8f20102dc62@loongson.cn>
 <a3e4cd0f-7500-b994-15b1-8df1cff24ab5@flygoat.com>
Message-ID: <f901dcdc-9724-a725-87ca-afe2aa216a94@flygoat.com>
Date:   Mon, 2 Nov 2020 18:47:50 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.4.0
MIME-Version: 1.0
In-Reply-To: <a3e4cd0f-7500-b994-15b1-8df1cff24ab5@flygoat.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk


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@loongson.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