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

[Lukas Wunner <lukas@wunner.de>]

On Wed, Jun 25, 2025 at 08:43:45PM +0200, Hans de Goede wrote:
> On 25-Jun-25 4:33 PM, Lukas Wunner wrote:
> > So how do you know that all of these unsupported devices have
> > PCI_CLASS_BRIDGE_HOST?
> 
> The top of the driver says
> 
>  * This is a GART driver for the AMD Opteron/Athlon64 on-CPU northbridge.
>  * It also includes support for the AMD 8151 AGP bridge
> 
> Note this only talks about north bridges.
> 
> Also given the age of AGP, I would expect the agp_amd64_pci_table[]
> to be pretty much complete and the need for probing for unknown AGP
> capable bridges is likely a relic which can be disabled by default.
> 
> Actually the amd64-agp code is weird in that has support for
> unknown AGP bridges enabled by default in the first place.
> 
> The global probe unknown AGP bridges bool which is called
> agp_try_unsupported_boot is false by default.
> 
> As discussed in the thread with my patch, we should probably
> just change the AMD specific agp_try_unsupported to default
> to false too.

Since the breaking change (causing the annoying message) was introduced
in this cycle, I think we should err on the side of caution and avoid
the risk of creating new regressions, if at all possible.

However if you are willing to deal with potential fallout, I would like
to encourage you to set "agp_try_unsupported = 0" (which the Kconfig
help text suggests is already the case) as a patch for the next cycle.

If you could give v2 of my (just submitted) patch a spin and respond
with a Tested-by on success, I'd be grateful.  I think this could go
in either through drm-misc-fixes or pci/for-linus (since the offending
commit went in through the pci tree).

Thanks!

Lukas