linux-kernel - Re: [PATCH v2 1/3] rust: pci: provide access to PCI Class, subclass, implementation values

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Message-Id: <DC5N439ZNA6E.34LSQ3K5366P7@kernel.org>
Date: Mon, 18 Aug 2025 16:57:37 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "John Hubbard" <jhubbard@...dia.com>
Cc: "Alexandre Courbot" <acourbot@...dia.com>, "Joel Fernandes"
 <joelagnelf@...dia.com>, "Timur Tabi" <ttabi@...dia.com>, "Alistair Popple"
 <apopple@...dia.com>, "David Airlie" <airlied@...il.com>, "Simona Vetter"
 <simona@...ll.ch>, "Bjorn Helgaas" <bhelgaas@...gle.com>,
 Krzysztof Wilczyński <kwilczynski@...nel.org>, "Miguel
 Ojeda" <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>, "Boqun
 Feng" <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Benno Lossin"
 <lossin@...nel.org>, "Andreas Hindborg" <a.hindborg@...nel.org>, "Alice
 Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>,
 <nouveau@...ts.freedesktop.org>, <linux-pci@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>, "LKML" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] rust: pci: provide access to PCI Class,
 subclass, implementation values

On Mon Aug 18, 2025 at 3:33 AM CEST, John Hubbard wrote:
> +            /// Create a `Class` from the raw class code value, or `None` if the value doesn't
> +            /// match any known class.
> +            pub fn from_u32(value: u32) -> Option<Self> {
> +                match value {
> +                    $(x if x == Self::$variant.0 => Some(Self::$variant),)+
> +                    _ => None,
> +                }
> +            }

Additional to the comments from Alex, I think one should be
`impl TryFrom<u32> for Class`.

> +
> +    /// 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 {
> +        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 +600,18 @@ 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 class_code_raw(&self) -> u32 {
> +        // SAFETY: `self.as_raw` is a valid pointer to a `struct pci_dev`.
> +        unsafe { (*self.as_raw()).class }
> +    }
> +
> +    /// Returns the PCI class as a `Class` struct, or `None` if the class code is invalid.
> +    pub fn class_enum(&self) -> Option<Class> {
> +        Class::from_u32(self.class_code_raw())
> +    }

I don't think we have struct pci_dev instances without a valid class code,
can we? Maybe we should convert infallibly here.