Re: [PATCH] agp/amd64: Bind to unsupported devices only if AGP is present

[Lukas Wunner <lukas@wunner.de>]

On Sat, Jun 21, 2025 at 03:51:44PM +0200, Ben Hutchings wrote:
> On Sat, 2025-06-21 at 14:29 +0200, Lukas Wunner wrote:
> > On Sat, Jun 21, 2025 at 02:07:40PM +0200, Ben Hutchings wrote:
> > > On Sat, 2025-06-21 at 11:40 +0200, Lukas Wunner wrote:
> > > > Since commit 172efbb40333 ("AGP: Try unsupported AGP chipsets on x86-64 by
> > > > default"), the AGP driver for AMD Opteron/Athlon64 CPUs attempts to bind
> > > > to any PCI device.
> > > > 
> > > > On modern CPUs exposing an AMD IOMMU, this results in a message with
> > > > KERN_CRIT severity:
> > > > 
> > > >   pci 0000:00:00.2: Resources present before probing
> > > > 
> > > > The driver used to bind only to devices exposing the AGP Capability, but
> > > > that restriction was removed by commit 6fd024893911 ("amd64-agp: Probe
> > > > unknown AGP devices the right way").
> > > 
> > > That didn't remove any restriction as the probe function still started
> > > by checking for an AGP capability.  The change I made was that the
> > > driver would actually bind to devices with the AGP capability instead of
> > > starting to use them without binding.
> > 
> > The message above would not be emitted without your change.
> > 
> > The check for the AGP capability in agp_amd64_probe() is too late
> > to prevent the message.  That's because the message is emitted
> > before ->probe() is even called.
> 
> I understand that.  But I don't feel that the explanation above
> accurately described the history here.

So please propose a more accurate explanation.

Thanks,

Lukas