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

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Message-ID: <CAH5fLgixvBWSf-3WDRj=Mxtn4ArQLqdKqMF0aSxyC6xVNPfTFQ@mail.gmail.com>
Date: Tue, 10 Dec 2024 11:55:33 +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 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.

Alice