Re: [PATCH] gpu: nova-core: fix aux device registration for multi-GPU systems

["Danilo Krummrich" <dakr@kernel.org>]

On Thu Feb 5, 2026 at 2:48 PM CET, Matthew Wilcox wrote:
> On Thu, Feb 05, 2026 at 01:44:27PM +0000, Gary Guo wrote:
>> > Fix this by using an atomic counter to generate unique IDs for each
>> > GPU's aux device registration. The TODO item to eventually use XArray
>> > for recycling aux device IDs is retained, but for now, this works very
>> > nicely.
>> >
>> > This has the side effect of making debugfs[1] work on multi-GPU systems.
>> 
>> Hi John,
>> 
>> Looks like this is something that should be achieved via IDA?
>
> Yes, if you have no need to go from ID to pointer, an IDA is better.
> That said, as far as I understand what this code is doing, an atomic_t
> solves the problem just fine and is cheaper.

I agree, for now an atomic should be perfectly fine. Though, with enough
patience binding/unbinding the driver from sysfs you can probably make this
overflow. :)

The reason for the Xarray TODO is that it is one option for a place where
nova-core can store nova-drm / vGPU specific data, once either vGPU or nova-drm
attaches to the auxiliary device. But I think there may be better alternatives.