The common practice in C drivers is to store pointers into `driver_data`
field of device IDs. The Rust code is however currently storing indices
into the fields and then carry a side table that maps the index to
pointers.
It is much simpler to just have `DeviceId` carry the pointer like C code
does. However, just doing so naively would cause a "pointers cannot be cast
to integers during const eval" error, as kernel_ulong_t does not have
provenance while pointers do, and Rust forbids `expose_provenance` during
consteval.
Work around this limitation by wrapping raw IDs in `MaybeUninit`.
`MaybeUninit` is allowed to host arbitrary bytes with or without
provenance, so we can just then use `unsafe` to store a pointer with
provenance there. This has the same effect as changing the C-side
definition to use `void*` instead of `kernel_ulong_t`, but without actually
changing the C side.
Signed-off-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/20260629-id_info-v2-8-56fccbe9c5ef@garyguo.net
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
0b76335e8f