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Subject: Re: [PATCH v5 3/6] LoongArch: KVM: Add cpucfg area for kvm hypervisor
To: Xi Ruoyao <xry111@xry111.site>, Jiaxun Yang <jiaxun.yang@flygoat.com>,
 Huacai Chen <chenhuacai@kernel.org>
Cc: Tianrui Zhao <zhaotianrui@loongson.cn>, Juergen Gross <jgross@suse.com>,
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 kvm@vger.kernel.org
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From: maobibo <maobibo@loongson.cn>
Message-ID: <e04a527b-2d9d-cfcd-e6ed-e8bd390649dd@loongson.cn>
Date: Tue, 27 Feb 2024 17:52:33 +0800
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On 2024/2/27 下午5:05, Xi Ruoyao wrote:
> On Tue, 2024-02-27 at 15:09 +0800, maobibo wrote:
> 
>> It is difficult to find an area unused by HW for CSR method since the
>> small CSR ID range.
> 
> We may use IOCSR instead.  In kernel/cpu-probe.c there are already some
> IOCSR reads.

yes, IOCSR can be used and one IOCSR area will be reserved for software. 
In general CSR/CPUCFG is to describe CPU features and IOCSR is to 
describe board/device features.

CSR area is limited to 16K, it is difficult for HW guys to reserve 
special area for software usage. IOCSR/CPUCFG is possible however.

Regards
Bibo Mao
> 
>> It is difficult to find an area unused by HW for CSR method since the
>> small CSR ID range. However it is easy for cpucfg. Here I doubt whether
>> you really know about LoongArch LVZ.
> 
> It's unfair to accuse the others for not knowing about LVZ considering
> the lack of public documentation.
>