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

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Message-ID: <Z1bKA5efDYxd8sTC@pollux.localdomain>
Date: Mon, 9 Dec 2024 11:44:19 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
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 Fri, Dec 06, 2024 at 03:01:18PM +0100, Alice Ryhl wrote:
> 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.

Yeah, but then every bus device has to re-implement the refcount dance we
already have in `device::Device` for the underlying base `struct device`.

I forgot to mention this in my previous reply to Boqun, but we even documented
it this way in `device::Device` [1].

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/rust/kernel/device.rs#n28

> 
> 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
> >