Re: [PATCH v1 2/3] rust: core abstractions for HID drivers

[Danilo Krummrich <dakr@kernel.org>]

On Sat, Jul 05, 2025 at 07:31:21AM +0000, Rahul Rameshbabu wrote:
> In parallel, I am thinking about how to design a Drop trait for handling
> HID device unplug instead of needing a C style remove callback. This
> will be crucial for implementing sophisticated leaf drivers.

Please have a look at how other bus abstractions are implemented, e.g. platform,
pci, auxiliary.

They all have a probe() function in the Driver trait, which returns a
Pin<KBox<Self>>, i.e. the drivers private data.

This ForeignOwnable is then stored in the private data pointer of the C struct
device, which I'm adding generic accessors for in [1].

On driver remove() this ForeignOwnable is extracted back into a Pin<KBox<Self>>
and dropped.

This means there's already Driver::drop() which is called on device unplug.

However, this is not sufficient, because Driver::drop() only gives you a &mut
self, i.e. a reference to Pin<KBox<Self>>, but not a Core context reference to
the Device, i.e. &Device<Core>. Hence you need a separate Driver::unbind()
callback. Please see [2] for that.

[1] https://lore.kernel.org/all/20250621195118.124245-3-dakr@kernel.org/
[2] https://lore.kernel.org/all/20250621195118.124245-7-dakr@kernel.org/