linux-kernel - Re: [PATCH v3 11/16] rust: pci: add basic PCI device / driver abstractions

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Message-ID: <Zx7B4Y5iegKVXpC4@Boquns-Mac-mini.local>
Date: Sun, 27 Oct 2024 15:42:41 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: gregkh@...uxfoundation.org, rafael@...nel.org, bhelgaas@...gle.com,
	ojeda@...nel.org, alex.gaynor@...il.com, gary@...yguo.net,
	bjorn3_gh@...tonmail.com, benno.lossin@...ton.me, tmgross@...ch.edu,
	a.hindborg@...sung.com, aliceryhl@...gle.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,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v3 11/16] rust: pci: add basic PCI device / driver
 abstractions

Hi Danilo,

On Tue, Oct 22, 2024 at 11:31:48PM +0200, Danilo Krummrich wrote:
[...]
> +/// 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>);
> +

Similar to https://lore.kernel.org/rust-for-linux/ZgG7TlybSa00cuoy@boqun-archlinux/

Could you also avoid wrapping a point to a PCI device? Instead, wrap the
object type:

    #[repr(transparent)]
    pub struct Device(Opaque<bindings::pci_dev>);

    impl AlwaysRefCounted for Device {
        <put_device() and get_device() on ->dev>
    }

Regards,
Boqun

> +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
> +    }
> +}
> -- 
> 2.46.2
> 
>