Re: [PATCH v3 01/13] gpu: nova-core: Set correct DMA mask

[Alistair Popple]

On 2025-09-30 at 23:29 +1000, Danilo Krummrich <dakr@xxxxxxxxxx> wrote...
> On 9/30/25 3:16 PM, Alistair Popple wrote:
> > +        // SAFETY: No DMA allocations have been made yet
> > +        unsafe { pdev.dma_set_mask_and_coherent(DmaMask::new::<47>())? };
> 
> I think you forgot to derive the value from the relevant sources, i.e. physical
> bus, DMA controller and MMU capabilities.
> 
> I assume not all GPU architectures / generations have the exact same capabilities?

Right. Long term we need a HAL for this, and I believe John was going to look
at that. In the short term everything we care about supports the same 47-bit
address width. And when I say "everything" I mean Turing and Ampere, although
I'm pretty sure 47-bits goes back to at least Pascal.

Newer GPU architectures (Hopper+) support greater widths (52-bits), but there's
no real impact to constraining these for now until a proper HAL is in place.

And that sounds like an excellent addition that I should make to the commit
logs and/or the comment on the constant definition, which fell off my radar when
reworking the rest of this series but will fix for v4.