linux-kernel - Re: [PATCH v4 15/15] s390: doc: detailed specifications for AP virtualization

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Message-Id: <53283f8e-52b5-5653-044c-843b5b033a1e@linux.vnet.ibm.com>
Date:   Tue, 17 Apr 2018 18:25:50 +0200
From:   Pierre Morel <pmorel@...ux.vnet.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        cohuck@...hat.com, kwankhede@...dia.com,
        bjsdjshi@...ux.vnet.ibm.com, pbonzini@...hat.com,
        alex.williamson@...hat.com, alifm@...ux.vnet.ibm.com,
        mjrosato@...ux.vnet.ibm.com, jjherne@...ux.vnet.ibm.com,
        thuth@...hat.com, pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com
Subject: Re: [PATCH v4 15/15] s390: doc: detailed specifications for AP
 virtualization

On 17/04/2018 18:14, Tony Krowiak wrote:
> On 04/16/2018 09:13 AM, Pierre Morel wrote:
>> On 15/04/2018 23:22, Tony Krowiak wrote:
>>> This patch provides documentation describing the AP architecture and
>>> design concepts behind the virtualization of AP devices. It also
>>>
...snip...
>>> +The process for reserving an AP queue for use by a KVM guest is:
>>> +
>>> +* The vfio-ap driver during its initialization will perform the 
>>> following:
>>> +  * Create the 'vfio_ap' root device - /sys/devices/vfio_ap
>>> +  * Create the 'matrix' device in the 'vfio_ap' root
>>> +  * Register the matrix device with the device core
>>> +* Register with the ap_bus for AP queue devices of type CEX4, CEX5 and
>>> +  CEX6 and to provide the vfio_ap driver's probe and remove 
>>> callback interfaces.
>>
>> I wonder why the type of card has anything to do with this driver.
>> It should be transparent, the driver should be able to provide the 
>> matrix (APM/AQM/ADM)
>> independently from the type of card in the slot.
>
> We've been down this road several times before. We are only supporting 
> virtualization of
> CEX4 and newer cards. Also, the AP bus requires registering for 
> specific card types.

Yes I know, but the AP BUS design may be not the optimal for the AP Matrix.
The AP Matrix is device independent.
We just write/clear bits in a matrix and we do not care what is plugged.

So may be make clear that this device dependence is due to the actual AP 
BUS interface design.

>
>>
>>
>> Regards,
>>
>> Pierre
>>
>

-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany