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Subject: Re: [PATCH 10/35] irqchip/gic-v4.1: VPE table (aka GICR_VPROPBASER)
 allocation
To:     Marc Zyngier <maz@kernel.org>, <kvmarm@lists.cs.columbia.edu>,
        <linux-kernel@vger.kernel.org>
CC:     Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Jason Cooper <jason@lakedaemon.net>,
        Thomas Gleixner <tglx@linutronix.de>
References: <20190923182606.32100-1-maz@kernel.org>
 <20190923182606.32100-11-maz@kernel.org>
 <155660c2-7f30-e188-ca8d-c37fabea6d97@huawei.com>
 <6f4ccdfd-4b63-04cb-e7c0-f069e620127f@kernel.org>
 <14111988-74c9-12c3-1322-1580ff6ba11f@huawei.com>
 <c4d63ccd-b5b2-007f-6174-1a9d20f3669d@kernel.org>
From:   Zenghui Yu <yuzenghui@huawei.com>
Message-ID: <56ddfedd-5d8c-0507-c164-b04d63f51a1e@huawei.com>
Date:   Fri, 27 Sep 2019 09:59:16 +0800
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On 2019/9/26 23:57, Marc Zyngier wrote:
> On 26/09/2019 16:19, Zenghui Yu wrote:
>> On 2019/9/25 22:41, Marc Zyngier wrote:
>>>
>>> Indeed. The whole idea is that ITSs and RDs can share a vPE table if
>>> they are in the same affinity group (such as a socket, for example).
>>> This is what is missing from v4.0 where the ITS knows about vPEs, but
>>> doesn't know about residency. With that in place, the HW is able to do a
>>> lot more for us.
>>
>> Thanks for your education!
>>
>> I really want to know *how* does GICv4.1 ITS know about the vPE
>> residency (in hardware level)?
> 
> Hey, I'm a SW guy, I don't design the hardware! ;-)
> 
>> I can understand that Redistributor can easily achieve it by
>> VPENDBASER's Valid and vPEID field.  And it's necessary for ITS to
>> know the residency so that it can determine whether it's appropriate
>> to trigger default doorbell for vPE.  But I have no knowledge about
>> how can it be achieved in hardware details.
> 
> My take is that the RD and the ITS can communicate over the shared
> table, hence my remark above about SVPET==0. But as I said, I'm not a HW
> guy.

;-) I should have asked our GIC engineers for these things.


Thanks,
zenghui