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

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Message-ID: <Z1jC7NnmwidLPT9Z@pollux>
Date: Tue, 10 Dec 2024 23:38:36 +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 Tue, Dec 10, 2024 at 11:55:33AM +0100, Alice Ryhl wrote:
> On Mon, Dec 9, 2024 at 11:44 AM Danilo Krummrich <dakr@...nel.org> wrote:
> >
> > 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
> 
> We could perhaps write a derive macro for AlwaysRefCounted that
> delegates to the inner type? That way, we can have the best of both
> worlds.

Sounds interesting, how exactly would this work?

(I'll already send out a v5, but let's keep discussing this.)

> 
> Alice