Re: [PATCH v7 4/4] gpu: nova-core: add boot42 support for next-gen GPUs

["Alexandre Courbot" <acourbot@nvidia.com>]

On Fri Nov 14, 2025 at 5:16 AM JST, John Hubbard wrote:
> On 11/13/25 11:59 AM, Joel Fernandes wrote:
>> Hi John,
>> 
> ...
>>> -        Spec::try_from(boot0)
>>> +        if boot0.is_older_than_fermi() {
>>> +            return Err(ENOTSUPP);
>>> +        }
>>> +
>>> +        Spec::try_from(regs::NV_PMC_BOOT_42::read(bar))
>> 
>> There is an inconsistency in error return here, if NV04 through NV50, it returns
>> -ENOTSUPP. For Fermi through Volta, it will read boot42 but will return -ENODEV
>> because `Spec::try_from()` -> `boot42.chipset()` with return -ENODEV. I am Ok
>> with either error return, but it would be good to make it consistent.
>> 
>
> Yes, good catch. It should be -ENOTSUPP for sure.
>
>> There also does not seem to be a diagnostic if the chipset is not supported. It
>> would be good diagnostic that the chipset did not match, right now it will
>> return -ENODEV, which could mean the device does not exist. -ENOTSUPP is better
>> though but an actual dmesg error message would be nice.
>
> Yes. The "not supported" case would happen in two situations:
>
> a) Someone found a pre-Fermi GPU to use for (probably) display, and they
> also have a Turing+ GPU in the same system (!), and they have both Nouveau
> and Nova drivers available.
>
> Here, it's not really an error situation. If this actually works, then
> Nova not supporting the older GPU is just expected operation.
>
> But these older GPUs are not even really directly supported, so this
> is a fringe case anyway.
>
> b) A newer GPU is installed, and Nova does not yet support it. Here,
> an error message is OK, because Nova is eventually (soon) going to 
> support that GPU.
>
> So I think that means an error message is reasonable here.
>
>> 
>> With these,
>> 
>> Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
>> 
>
> Thanks for the review!
>
> Alex, I think I'd better re-spin and re-test, in order to safely collect
> the various small fixes from you and Joel. I can do that today.

Agreed, that will limit the risk of me not capturing everything
properly. Thanks!