Re: [PATCH v8 05/31] gpu: nova-core: set DMA mask width based on GPU architecture

[Alexandre Courbot]

On Tue, 24 Mar 2026 20:52:16 -0700, John Hubbard <jhubbard@xxxxxxxxxx> wrote:
> diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driver.rs
> index 84b0e1703150..41227d29934e 100644
> --- a/drivers/gpu/nova-core/driver.rs
> +++ b/drivers/gpu/nova-core/driver.rs
> @@ -84,18 +78,20 @@ fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> impl PinInit<Self, E
> [ ... skip 13 lines ... ]
> +            dev_info!(pdev, "NVIDIA ({})\n", spec);
> +
> +            // SAFETY: No concurrent DMA allocations or mappings can be made because
> +            // the device is still being probed and therefore isn't being used by
> +            // other threads of execution.
> +            unsafe { pdev.dma_set_mask_and_coherent(spec.chipset().arch().dma_mask())? };

To limit the unsafe block to unsafe operations, we should store the DMA
mask into a local variable.

>
> diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
> index 3cd7709883be..e7c3860cfb28 100644
> --- a/drivers/gpu/nova-core/gpu.rs
> +++ b/drivers/gpu/nova-core/gpu.rs
> @@ -162,6 +163,16 @@ pub(crate) enum Architecture {
>      Blackwell = 0x1b,
>  }
>  
> +impl Architecture {
> +    /// Returns the DMA mask supported by this architecture.
> +    pub(crate) const fn dma_mask(&self) -> DmaMask {
> +        match self {
> +            Self::Turing | Self::Ampere | Self::Ada => DmaMask::new::<47>(),
> +            Self::Hopper | Self::Blackwell => DmaMask::new::<52>(),
> +        }
> +    }
> +}

Eventually we may want to move this to the `Gpu` HAL, but let's do that
as a follow-up patch if we find it is relevant (which I am not sure
about yet).

> @@ -295,32 +306,32 @@ pub(crate) fn new<'a>(
>          pdev: &'a pci::Device<device::Bound>,
>          devres_bar: Arc<Devres<Bar0>>,
>          bar: &'a Bar0,
> +        spec: Spec,
>      ) -> impl PinInit<Self, Error> + 'a {
> -        try_pin_init!(Self {
> -            spec: Spec::new(pdev.as_ref(), bar).inspect(|spec| {
> -                dev_info!(pdev, "NVIDIA ({})\n", spec);
> -            })?,
> +        let chipset = spec.chipset();

`spec` is now `Copy`, so we don't need this local variable anymore.
Removing it and accessing `spec.chipset` directly simplifies the
remainder of the diff.

-- 
Alexandre Courbot <acourbot@xxxxxxxxxx>