Re: [PATCH 1/2] rust: pci: add domain_nr() accessor

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

On Tue Nov 10, 2026 at 4:36 AM CET, John Hubbard wrote:
> The nova-core driver has to send the GPU's PCI location to the GPU's
> firmware as one word that holds the domain, the bus and the device
> number.
>
> The PCI abstraction has dev_id(), which packs the bus, the device and
> the function into one value. It has no accessor that reports the domain.
>
> Add an accessor for the domain number.
>
> Suggested-by: Miguel Ojeda <ojeda@kernel.org>

Is this tag intentional? (Just asking since my tooling flagged it as it wasn't
present in the first submission of this patch and some other criteria.)

> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  rust/helpers/pci.c |  5 +++++
>  rust/kernel/pci.rs | 14 ++++++++++++++
>  2 files changed, 19 insertions(+)
>
> diff --git a/rust/helpers/pci.c b/rust/helpers/pci.c
> index a8540f90b13c..49f2c089d236 100644
> --- a/rust/helpers/pci.c
> +++ b/rust/helpers/pci.c
> @@ -7,6 +7,11 @@ __rust_helper u16 rust_helper_pci_dev_id(struct pci_dev *dev)
>  	return PCI_DEVID(dev->bus->number, dev->devfn);
>  }
>  
> +__rust_helper int rust_helper_pci_domain_nr(struct pci_dev *dev)
> +{
> +	return pci_domain_nr(dev->bus);

Rust helpers should generally be transparent wrappers and not provide any
semantics, even if it is just to resolve a pointer.

> +}
> +
>  __rust_helper resource_size_t
>  rust_helper_pci_resource_start(struct pci_dev *pdev, int bar)
>  {
> diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
> index 769d01d23429..57718e48208d 100644
> --- a/rust/kernel/pci.rs
> +++ b/rust/kernel/pci.rs
> @@ -408,6 +408,20 @@ pub fn dev_id(&self) -> u16 {
>          unsafe { bindings::pci_dev_id(self.as_raw()) }
>      }
>  
> +    /// Returns the PCI domain number of the bus that this device is on.
> +    #[inline]
> +    pub fn domain_nr(&self) -> u32 {
> +        // SAFETY: By its type invariant `self.as_raw` is always a valid pointer to a
> +        // `struct pci_dev`.
> +        let domain_nr = unsafe { bindings::pci_domain_nr(self.as_raw()) };
> +
> +        // CAST: `pci_domain_nr()` returns an `int`, but a registered bus never has a negative
> +        // domain, because `pci_register_host_bridge()` fails when the domain allocation fails.
> +        // A negative value here is a kernel bug rather than a condition for a caller to handle.
> +        debug_assert!(domain_nr >= 0);
> +        domain_nr as u32

NIT: Please move the comment directly above the actual cast statement.

> +    }