linux-kernel - Re: [PATCH 09/11] PCI: add matching checks for driver

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Date:   Tue, 15 Jun 2021 20:32:57 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Max Gurtovoy <mgurtovoy@...dia.com>, cohuck@...hat.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        aviadye@...dia.com, oren@...dia.com, shahafs@...dia.com,
        parav@...dia.com, artemp@...dia.com, kwankhede@...dia.com,
        ACurrid@...dia.com, cjia@...dia.com, yishaih@...dia.com,
        kevin.tian@...el.com, hch@...radead.org, targupta@...dia.com,
        shameerali.kolothum.thodi@...wei.com, liulongfang@...wei.com,
        yan.y.zhao@...el.com
Subject: Re: [PATCH 09/11] PCI: add matching checks for driver_override
 binding

On Tue, Jun 15, 2021 at 05:22:42PM -0600, Alex Williamson wrote:

> > > b) alone is a functional, runtime difference.  
> > 
> > I would state b) differently:
> > 
> > b) Ignore the driver-override-only match entries in the ID table.
> 
> No, pci_match_device() returns NULL if a match is found that is marked
> driver-override-only and a driver_override is not specified.  That's
> the same as no match at all.  We don't then go on to search past that
> match in the table, we fail to bind the driver.  That's effectively an
> anti-match when there's no driver_override on the device.

anti-match isn't the intention. The deployment will have match tables
where all entires are either flags=0 or are driver-override-only.

I would say that mixed match tables make driver-override-only into an
anti-match is actually a minor bug in the patch.

The series isn't about adding some new anti-match scheme.

> I understand that's not your intended use case, but I think this allows
> that and justifies handling a dynamic ID the same as a static ID.
> Adding a field to pci_device_id, which is otherwise able to be fully
> specified via new_id, except for this field, feels like a bug.  Thanks,

Okay, I see what you are saying clearly now.

Your example usage seems legit to me, but I really don't want to
entangle it with this series. It is a seperate idea, it can go as a
seperate work that uses the new flags and an updated new_id and
related parts by someone who wants it.

I hope you'll understand that having NVIDIA Mellanox persue what you
describe above is just not going to work..

Jason