On Wed, Oct 30, 2024 at 7:07 PM Danilo Krummrich <dakr@xxxxxxxxxx> wrote:
>
> On Wed, Oct 30, 2024 at 04:50:43PM +0100, Alice Ryhl wrote:
> > On Tue, Oct 22, 2024 at 11:33 PM Danilo Krummrich <dakr@xxxxxxxxxx> wrote:
> > > +/// Drivers must implement this trait in order to get a platform driver registered. Please refer to
> > > +/// the `Adapter` documentation for an example.
> > > +pub trait Driver {
> > > + /// The type holding information about each device id supported by the driver.
> > > + ///
> > > + /// TODO: Use associated_type_defaults once stabilized:
> > > + ///
> > > + /// type IdInfo: 'static = ();
> > > + type IdInfo: 'static;
> > > +
> > > + /// The table of device ids supported by the driver.
> > > + const ID_TABLE: IdTable<Self::IdInfo>;
> > > +
> > > + /// Platform driver probe.
> > > + ///
> > > + /// Called when a new platform device is added or discovered.
> > > + /// Implementers should attempt to initialize the device here.
> > > + fn probe(dev: &mut Device, id_info: Option<&Self::IdInfo>) -> Result<Pin<KBox<Self>>>;
> >
> > This forces the user to put their driver data in a KBox, but they
> > might want to use an Arc instead. You don't actually *need* a KBox -
> > any ForeignOwnable seems to fit your purposes.
>
> This is intentional, I do need a `KBox` here.
>
> The reason is that I want to enforce that the returned `Pin<KBox<Self>>` has
> exactly the lifetime of the binding of the device and driver, i.e. from probe()
> until remove(). This is the lifetime the structure should actually represent.
>
> This way we can attach things like `Registration` objects to this structure, or
> anything else that should only exist from probe() until remove().
>
> If a driver needs some private driver data that needs to be reference counted,
> it is usually attached to the class representation of the driver.
>
> For instance, in Nova the reference counted stuff is attached to the DRM device
> and then I just have the DRM device (which itself is reference counted) embedded
> in the `Driver` structure.
>
> In any case, drivers can always embed a separate `Arc` in their `Driver`
> structure if they really have a need for that.
Is this needed for soundness of those registrations?
Also, I've often seen drivers use devm_kzalloc or similar to allocate
exactly this object. KBox doesn't allow for that.
Alice
