Re: [PATCH v7 02/21] target/loongarch: Add core definition

From: Song Gao <gaosong@loongson.cn>
To: "Richard Henderson" <richard.henderson@linaro.org>,
	"WANG Xuerui" <i.qemu@xen0n.name>,
	"Philippe Mathieu-Daudé" <f4bug@amsat.org>,
	qemu-devel@nongnu.org, karl@freefriends.org
Cc: peter.maydell@linaro.org, thuth@redhat.com,
	qemu-devel-owner@nongnu.org, yangxiaojuan@loongson.cn,
	peterx@redhat.com, laurent@vivier.eu, alistair.francis@wdc.com,
	maobibo@loongson.cn, pbonzini@redhat.com, bmeng.cn@gmail.com,
	alex.bennee@linaro.org, chenhuacai@loongson.cn
Subject: Re: [PATCH v7 02/21] target/loongarch: Add core definition
Date: Thu, 21 Oct 2021 11:21:16 +0800	[thread overview]
Message-ID: <49d356da-30dd-6460-73fa-8a9e165a9091@loongson.cn> (raw)
In-Reply-To: <da597248-8e06-2f14-b39e-67c457aa5a71@linaro.org>

Hi, all

On 10/20/2021 09:56 PM, Richard Henderson wrote:
> On 10/20/21 5:00 AM, WANG Xuerui wrote:
>> On 2021/10/20 16:54, Song Gao wrote:
>>
>>> On 10/19/2021 01:38 AM, Philippe Mathieu-Daudé wrote:
>>>> On 10/18/21 18:06, WANG Xuerui wrote:
>>>>
>>>> On 10/18/21 20:47, Song Gao wrote:
>>>>>> +static void set_loongarch_cpucfg(CPULoongArchState *env)
>>>>>> +{
>>>>>> +    int i;
>>>>>> +
>>>>>> +    for (i = 0; i < 49; i++) {
>>>>>> +        env->cpucfg[i] = 0x0;
>>>>>> +    }
>>>>>> +    env->cpucfg[0] = 0x14c010;
>>>>>> +    env->cpucfg[1] = 0x3f2f2fe;
>>>>>> +    env->cpucfg[2] = 0x60c3cf;
>>>>>> +    env->cpucfg[3] = 0xcff;
>>>>>> +    env->cpucfg[4] = 0x5f5e100;
>>>>>> +    env->cpucfg[5] = 0x10001;
>>>>>> +    env->cpucfg[16] = 0x2c3d;
>>>>>> +    env->cpucfg[17] = 0x6080003;
>>>>>> +    env->cpucfg[18] = 0x6080003;
>>>>>> +    env->cpucfg[19] = 0x60800f;
>>>>>> +    env->cpucfg[20] = 0x60f000f;
>>>>> I know these values are taken from a real 3A5000 chip, since I have such
>>>>> a machine and I've done the experiment, but others likely wouldn't
>>>>> notice so quickly. Maybe put some comment on top of this function to
>>>>> illustrate this?
>>>> Simpler: ...
>>>>
>>> On linux-user emulation. We don't care about the value of cpucfg[i].
>>> I think we only need to set cpucfg[i] to 0. and set value on system emulations, is that better?
>>
>> I'm afraid that wouldn't be better; actually it would be *wrong* to just
>> return zeroes for user-space CPUCFG accesses. CPUCFG is designed to
>> provide runtime feature probing like CPUID, and is usable from
>> user-space. So, one can only assume this data is being used, and
>> properly return data.
>>
>> I've heard that kernel could choose to not actually enable all features
>> for which CPUCFG indicate support, while not configuring CPUCFG values
>> to reflect that, thus making CPUCFG values unreliable; that's not a
>> proper reason to return zeroes. Kernel should be fixed to properly
>> configure CPUCFG instead. Because otherwise you wouldn't make such an
>> instruction an unprivileged one in the first place...
> 
> In the meantime, I think you really need to filter these values to those you have implemented.  E.g. cpucfg[2].LASX here indicates support for the 256-bit vector extension.  Similarly the COMPLEX and CRYPTO extensions.
> 
> I think you would do well to add some FIELD definitions so that these can be set symbolically.
>
OK.

BTW,   

Account yangxiaojuan@loongson.cn It seems that she has been blacklisted. Xiaojuan sent 31 e-mails, which were not displayed since the 21st one, people who don't have a CC can't read all the emails,  and xiaojuan reply can't be in qemu-level@nongnu.org. 

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Xuerui said: 

"You may address the several review comments then just send v2. This way
the threading is less likely to be damaged (you need to exactly specify
In-Reply-To headers and such for the re-sent patches to correctly link
to this thread, I think it's not worth the effort). "

I think this will have the same problem. 

Richard and Karl,  How can we solve this problem？

Thanks
Song Gao.

> 
> r~