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

Danilo Krummrich
2024-12-11T14:32:30Z

On Wed, Dec 11, 2024 at 02:06:50PM +0100, Alice Ryhl wrote:
> On Tue, Dec 10, 2024 at 11:38 PM Danilo Krummrich <dakr@kernel.org> wrote:
> >
> > 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@kernel.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@kernel.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@gmail.com>
> > > > > > Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
> > > > > > Signed-off-by: Danilo Krummrich <dakr@kernel.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.)
>
> Well, the derive macro could assume that the refcount is manipulated
> in the same way as the inner type does it. I admit that the idea is
> not fully formed, but if we can avoid wrapping ARef, that would be
> ideal.

If we can get this to work, I agree it's a good solution.

What do you think about making this a follow up of this series?

> It sounds like the only reason you don't do that is that it's
> more unsafe, which the macro could reduce.

Exactly, yes.

>
>
> Alice