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

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 25-Jun-25 8:43 PM, Hans de Goede wrote:
> Hi,
> 
> On 25-Jun-25 4:33 PM, Lukas Wunner wrote:
>> On Wed, Jun 25, 2025 at 04:08:38PM +0200, Hans de Goede wrote:
>>> Lukas made me aware of this attempt to fix the KERN_CRIT msg, because
>>> I wrote a slightly different patch to fix this:
>>>
>>> https://lore.kernel.org/dri-devel/20250625112411.4123-1-hansg@kernel.org/
>>>
>>> This seems like a cleaner fix to me and something which would be good
>>> to have regardless since currently the driver_attach() call is doing
>>> too much work because the promisc table catches an unnecessary wide
>>> net / match matching many PCI devices which cannot be AGP capable
>>> at all.
>>
>> 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.
> 
>> The only thing we know is that an AGP
>> Capability must be present.
>>
>> In particular, AGP 3.0 sec 2.5 explicitly allows PCI-to-PCI bridges
>> in addition to Host-to-PCI bridges.
> 
> Ok, so we can add a second entry to the agp_amd64_pci_promisc_table[]
> to match PCI to PCI bridges just to be sure, that still feels
> cleaner to me.

ping? It would be good to get some consensus on how to
fix this and move forward with a fix. Either the patch from
this thread; or my patch:

https://lore.kernel.org/dri-devel/20250625112411.4123-1-hansg@kernel.org/

Works for me, the most important thing here is to get this
regression fixed.

Regards,

Hans