Re: [PATCH v3 2/2] gpu: nova-core: add boot42 support for next-gen GPUs

[John Hubbard]

On 10/29/25 6:07 PM, John Hubbard wrote:
> On 10/29/25 6:01 PM, Timur Tabi wrote:
> > On Wed, 2025-10-29 at 17:35 -0700, John Hubbard wrote:
> > >          // "Future" GPUs (some time after Rubin) will set 
> > > `architecture_0`
> > >          // to 0, and `architecture_1` to 1, and put the architecture 
> > > details in
> > >          // boot42 instead.
> >
> > I don't want to kick a dead horse here, but aren't the architecture 
> > details already in boot42
> > for Turing?  I thought the whole point was that we don't need boot0 
> > any more, and only Nouveau
> > has to worry about boot0 vs boot42.
>
> Yes, but someone can still plug in a pre-Turing GPU and try to
> boot up with nova-core.ko on the system.
>
> So it's important to avoid getting into trouble in that case.

In fact, here's what I have staged for the next posting:

impl Spec { 

    fn new(bar: &Bar0) -> Result<Spec> { 

        // Some brief notes about boot0 and boot42, in chronological 
order:
        // 

        // NV04 through Volta: 

        // 

        //    Not supported by Nova. boot0 is necessary and sufficient 
to identify these GPUs.
        //    boot42 may not even exist on some of these GPUs.boot42 

        // 

        // Turing through Blackwell: 

        // 

        //     Supported by both Nouveau and Nova. boot0 is still 
necessary and sufficient to
        //     identify these GPUs. boot42 exists on these GPUs but we 
don't need to use it.
        // 

        // Rubin: 

        // 

        //     Only supported by Nova. Need to use boot42 to fully 
identify these GPUs.
        // 

        // "Future" (after Rubin) GPUs: 

        // 

        //    Only supported by Nova. NV_PMC_BOOT's ARCH_0 (bits 28:24) 
will be zeroed out, and
        //    ARCH_1 (bit 8:8) will be set to 1, which will mean, 
"refer to NV_PMC_BOOT_42".
 

        let boot0 = regs::NV_PMC_BOOT_0::read(bar); 

 

        if boot0.use_boot42_instead() { 

            Spec::try_from(regs::NV_PMC_BOOT_42::read(bar)) 

        } else { 

            Spec::try_from(boot0) 

        } 

    } 

}