linux-kernel - Re: [PATCH 8/9] vfio/pci: export nvlink2 support into vendor vfio

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Date:   Thu, 11 Mar 2021 11:44:38 +0200
From:   Max Gurtovoy <mgurtovoy@...dia.com>
To:     Alexey Kardashevskiy <aik@...abs.ru>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     <alex.williamson@...hat.com>, <cohuck@...hat.com>,
        <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <liranl@...dia.com>, <oren@...dia.com>, <tzahio@...dia.com>,
        <leonro@...dia.com>, <yarong@...dia.com>, <aviadye@...dia.com>,
        <shahafs@...dia.com>, <artemp@...dia.com>, <kwankhede@...dia.com>,
        <ACurrid@...dia.com>, <cjia@...dia.com>, <yishaih@...dia.com>,
        <mjrosato@...ux.ibm.com>, <hch@....de>
Subject: Re: [PATCH 8/9] vfio/pci: export nvlink2 support into vendor vfio_pci
 drivers


On 3/11/2021 9:54 AM, Alexey Kardashevskiy wrote:
>
>
> On 11/03/2021 13:00, Jason Gunthorpe wrote:
>> On Thu, Mar 11, 2021 at 12:42:56PM +1100, Alexey Kardashevskiy wrote:
>>>>> btw can the id list have only vendor ids and not have device ids?
>>>>
>>>> The PCI matcher is quite flexable, see the other patch from Max for
>>>> the igd
>>>   ah cool, do this for NVIDIA GPUs then please, I just discovered 
>>> another P9
>>> system sold with NVIDIA T4s which is not in your list.
>>
>> I think it will make things easier down the road if you maintain an
>> exact list <shrug>
>
>
> Then why do not you do the exact list for Intel IGD? The commit log 
> does not explain this detail.

I expect Intel team to review this series and give a more precise list.

I did the best I could in finding a proper configuration for igd.


>
>
>>>> But best practice is to be as narrow as possible as I hope this will
>>>> eventually impact module autoloading and other details.
>>>
>>> The amount of device specific knowledge is too little to tie it up 
>>> to device
>>> ids, it is a generic PCI driver with quirks. We do not have a separate
>>> drivers for the hardware which requires quirks.
>>
>> It provides its own capability structure exposed to userspace, that is
>> absolutely not a "quirk"
>>
>>> And how do you hope this should impact autoloading?
>>
>> I would like to autoload the most specific vfio driver for the target
>> hardware.
>
>
> Is there an idea how it is going to work? For example, the Intel IGD 
> driver and vfio-pci-igd - how should the system pick one? If there is 
> no MODULE_DEVICE_TABLE in vfio-pci-xxx, is the user supposed to try 
> binding all vfio-pci-xxx drivers until some binds?

For example, in my local setup I did a POC patch that convert some 
drivers to be "manual binding only drivers".

So the IGD driver will have the priority, user will unbind the device 
from it, load igd-vfio-pci, bind the device to it, ends with probing.

For now we separated the driver core stuff until we all agree that this 
series is the right way to go + we also make sure it's backward compatible.

>
>
>> If you someday need to support new GPU HW that needs a different VFIO
>> driver then you are really stuck because things become indeterminate
>> if there are two devices claiming the ID. We don't have the concept of
>> "best match", driver core works on exact match.
>
>
>