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

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Date:   Thu, 11 Mar 2021 18:54:09 +1100
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Max Gurtovoy <mgurtovoy@...dia.com>, 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 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.


>>> 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?


> 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.



-- 
Alexey