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

[John Hubbard <jhubbard@nvidia.com>]

On 8/19/25 8:48 PM, Elle Rhumsaa wrote:
> On Sun, Aug 17, 2025 at 06:33:03PM -0700, John Hubbard wrote:
>> Allow callers to write Class::STORAGE_SCSI instead of
>> bindings::PCI_CLASS_STORAGE_SCSI, for example.
>>
>> New APIs:
>>      Class::STORAGE_SCSI, Class::NETWORK_ETHERNET, etc.
>>      Class::from_u32(), as_u32()
>>      Class::MASK_FULL, MASK_CLASS_SUBCLASS
>>      DeviceId::from_class_and_vendor()
>>      Device::class_code_raw(), class_enum()
>>
>> Cc: Danilo Krummrich <dakr@kernel.org>
>> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>> ---
>>   rust/kernel/pci.rs | 202 +++++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 202 insertions(+)
>>
>> diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
>> index 887ee611b553..9caa1d342d52 100644
>> --- a/rust/kernel/pci.rs
>> +++ b/rust/kernel/pci.rs
>> @@ -23,6 +23,179 @@
>>   };
>>   use kernel::prelude::*;
>>   
>> +macro_rules! define_all_pci_classes {
>> +    (
>> +        $($variant:ident = $binding:expr,)+
>> +    ) => {
>> +        /// Converts a PCI class constant to 24-bit format.
>> +        ///
>> +        /// Many device drivers use only the upper 16 bits (base class and subclass), but some
>> +        /// use the full 24 bits. In order to support both cases, store the class code as a 24-bit
>> +        /// value, where 16-bit values are shifted up 8 bits.
>> +        const fn to_24bit_class(val: u32) -> u32 {
>> +            if val > 0xFFFF { val } else { val << 8 }
>> +        }
>> +
>> +        /// 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).
>> +        ///
>> +        #[derive(Debug, Clone, Copy, PartialEq, Eq)]
>> +        #[repr(transparent)]
>> +        pub struct Class(u32);
>> +
>> +        impl Class {
>> +            $(
>> +                #[allow(missing_docs)]
>> +                pub const $variant: Self = Self(to_24bit_class($binding));
>> +            )+
>> +
>> +            /// Match the full class code.
>> +            pub const MASK_FULL: u32 = 0xffffff;
>> +
>> +            /// Match the upper 16 bits of the class code (base class and subclass only).
>> +            pub const MASK_CLASS_SUBCLASS: u32 = 0xffff00;
>> +
>> +            /// 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,
>> +                }
>> +            }
>> +
>> +            /// Get the raw 24-bit class code value.
>> +            pub const fn as_u32(self) -> u32 {
>> +                self.0
>> +            }
>> +        }
>> +    };
>> +}
>> +
>> +define_all_pci_classes! {
>> +    NOT_DEFINED                = bindings::PCI_CLASS_NOT_DEFINED,                // 0x000000
>> +
>> +    ...
>> +
>> +    OTHERS                     = bindings::PCI_CLASS_OTHERS,                     // 0xff0000
>> +}
>> +
>>   /// An adapter for the registration of PCI drivers.
>>   pub struct Adapter<T: Driver>(T);
>>   
>> @@ -157,6 +330,23 @@ 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 {
>> +        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())
>> +    }
>>   }
>>   
>>   impl Device<device::Bound> {
>> -- 
>> 2.50.1
> 
> All of the functions could probably be `#[inline]`ed, though I'm not
> sure how much it affects the `const` functions, since they're already
> evaluated at compile-time.

These are not in a hot path, which is why the other, similar functions
nearby are not inlined.

> 
> Reviewed-by: Elle Rhumsaa <elle@weathered-steel.dev>

Thanks for the review of the series!

thanks,
-- 
John Hubbard