linux-kernel - Re: [PATCH v4 08/13] rust: pci: add basic PCI device / driver abstractions

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Message-ID: <CAH5fLgh6qgQ=SBn17biSRbqO8pNtSEq=5fDY3iuGzbuf2Aqjeg@mail.gmail.com>
Date: Fri, 6 Dec 2024 15:01:18 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: gregkh@...uxfoundation.org, rafael@...nel.org, bhelgaas@...gle.com, 
	ojeda@...nel.org, alex.gaynor@...il.com, boqun.feng@...il.com, 
	gary@...yguo.net, bjorn3_gh@...tonmail.com, benno.lossin@...ton.me, 
	tmgross@...ch.edu, a.hindborg@...sung.com, airlied@...il.com, 
	fujita.tomonori@...il.com, lina@...hilina.net, pstanner@...hat.com, 
	ajanulgu@...hat.com, lyude@...hat.com, robh@...nel.org, 
	daniel.almeida@...labora.com, saravanak@...gle.com, dirk.behme@...bosch.com, 
	j@...nau.net, fabien.parent@...aro.org, chrisi.schrefl@...il.com, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v4 08/13] rust: pci: add basic PCI device / driver abstractions

On Thu, Dec 5, 2024 at 3:16 PM Danilo Krummrich <dakr@...nel.org> wrote:
>
> Implement the basic PCI abstractions required to write a basic PCI
> driver. This includes the following data structures:
>
> The `pci::Driver` trait represents the interface to the driver and
> provides `pci::Driver::probe` for the driver to implement.
>
> The `pci::Device` abstraction represents a `struct pci_dev` and provides
> abstractions for common functions, such as `pci::Device::set_master`.
>
> In order to provide the PCI specific parts to a generic
> `driver::Registration` the `driver::RegistrationOps` trait is implemented
> by `pci::Adapter`.
>
> `pci::DeviceId` implements PCI device IDs based on the generic
> `device_id::RawDevceId` abstraction.
>
> Co-developed-by: FUJITA Tomonori <fujita.tomonori@...il.com>
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>
> Signed-off-by: Danilo Krummrich <dakr@...nel.org>

> +/// The PCI device representation.
> +///
> +/// A PCI device is based on an always reference counted `device:Device` instance. Cloning a PCI
> +/// device, hence, also increments the base device' reference count.
> +#[derive(Clone)]
> +pub struct Device(ARef<device::Device>);

It seems more natural for this to be a wrapper around
`Opaque<bindings::pci_dev>`. Then you can have both &Device and
ARef<Device> depending on whether you want to hold a refcount or not.

Alice

> +impl Device {
> +    /// Create a PCI Device instance from an existing `device::Device`.
> +    ///
> +    /// # Safety
> +    ///
> +    /// `dev` must be an `ARef<device::Device>` whose underlying `bindings::device` is a member of
> +    /// a `bindings::pci_dev`.
> +    pub unsafe fn from_dev(dev: ARef<device::Device>) -> Self {
> +        Self(dev)
> +    }
> +
> +    fn as_raw(&self) -> *mut bindings::pci_dev {
> +        // SAFETY: By the type invariant `self.0.as_raw` is a pointer to the `struct device`
> +        // embedded in `struct pci_dev`.
> +        unsafe { container_of!(self.0.as_raw(), bindings::pci_dev, dev) as _ }
> +    }
> +
> +    /// Enable memory resources for this device.
> +    pub fn enable_device_mem(&self) -> Result {
> +        // SAFETY: `self.as_raw` is guaranteed to be a pointer to a valid `struct pci_dev`.
> +        let ret = unsafe { bindings::pci_enable_device_mem(self.as_raw()) };
> +        if ret != 0 {
> +            Err(Error::from_errno(ret))
> +        } else {
> +            Ok(())
> +        }
> +    }
> +
> +    /// Enable bus-mastering for this device.
> +    pub fn set_master(&self) {
> +        // SAFETY: `self.as_raw` is guaranteed to be a pointer to a valid `struct pci_dev`.
> +        unsafe { bindings::pci_set_master(self.as_raw()) };
> +    }
> +}
> +
> +impl AsRef<device::Device> for Device {
> +    fn as_ref(&self) -> &device::Device {
> +        &self.0
> +    }
> +}
> --
> 2.47.0
>