Re: [PATCH v3 1/3] rust: pci: provide access to PCI Class, subclass, implementation values

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

On Tue Aug 19, 2025 at 5:11 AM CEST, John Hubbard wrote:
> +/// PCI device class codes. Each entry contains the full 24-bit PCI
> +/// class code (base class in bits 23-16, subclass in bits 15-8,
> +/// programming interface in bits 7-0).
> +///
> +/// # Examples
> +///
> +/// ```
> +/// # use kernel::{device::Core, pci::{self, Class}, prelude::*};
> +/// fn probe_device(pdev: &pci::Device<Core>) -> Result<()> {
> +///     // Get the PCI class for this device
> +///     let pci_class = pdev.pci_class();
> +///     dev_info!(
> +///         pdev.as_ref(),
> +///         "Detected PCI class: (0x{:06x})\n",
> +///         pci_class.as_u32()
> +///     );

Maybe a bit cleaner to implement Display for pci::Class?

> +///     Ok(())
> +/// }
> +/// ```
> +#[derive(Debug, Clone, Copy, PartialEq, Eq)]
> +#[repr(transparent)]
> +pub struct Class(u32);

[ Class impl and lots of pci class ids... ]

I think we should move all this to a new Rust module (rust/kernel/pci/class.rs)
to keep this file reasonably small.

You can add

	use self::class::Class;
	use self::class::ClassMask;

in this file to make it appear as e.g. kernel::pci::Class.

Sorry I didn't mention this in the previous version.

>  /// An adapter for the registration of PCI drivers.
>  pub struct Adapter<T: Driver>(T);
>  
> @@ -157,6 +355,23 @@ pub const fn from_class(class: u32, class_mask: u32) -> Self {
>              override_only: 0,
>          })
>      }
> +
> +    /// Create a new `pci::DeviceId` from a class number, mask, and specific vendor.
> +    ///
> +    /// This is more targeted than [`DeviceId::from_class`]: in addition to matching by Vendor, it
> +    /// also matches the PCI Class (up to the entire 24 bits, depending on the mask).
> +    pub const fn from_class_and_vendor(class: Class, class_mask: u32, vendor: u32) -> Self {

I think it would be good if class_mask would be a new type ClassMask that only
has the constants that are applicable for this field, i.e. MASK_FULL and
MASK_CLASS_SUBCLASS.

> +        Self(bindings::pci_device_id {
> +            vendor,
> +            device: DeviceId::PCI_ANY_ID,
> +            subvendor: DeviceId::PCI_ANY_ID,
> +            subdevice: DeviceId::PCI_ANY_ID,
> +            class: class.as_u32(),
> +            class_mask,
> +            driver_data: 0,
> +            override_only: 0,
> +        })
> +    }
>  }
>  
>  // SAFETY: `DeviceId` is a `#[repr(transparent)]` wrapper of `pci_device_id` and does not add
> @@ -410,6 +625,18 @@ pub fn resource_len(&self, bar: u32) -> Result<bindings::resource_size_t> {
>          // - by its type invariant `self.as_raw` is always a valid pointer to a `struct pci_dev`.
>          Ok(unsafe { bindings::pci_resource_len(self.as_raw(), bar.try_into()?) })
>      }
> +
> +    /// Returns the full 24-bit PCI class code as stored in hardware.
> +    /// This includes base class, subclass, and programming interface.
> +    pub fn pci_class_code_raw(&self) -> u32 {
> +        // SAFETY: `self.as_raw` is a valid pointer to a `struct pci_dev`.
> +        unsafe { (*self.as_raw()).class }
> +    }

Do we need this method? I think drivers can just call pdev.pci_class().as_u32()
instead (which we could also name as_raw()).

> +    /// Returns the PCI class as a `Class` struct.
> +    pub fn pci_class(&self) -> Class {
> +        Class(self.pci_class_code_raw())
> +    }

This is good! At a first glance the name looks a bit odd or redundant, but
people would clearly expect something different when this is called as
pdev.class() (i.e. a struct class representation).