After some discussions on the list [1] and the Rust libs team [2], this patchset undergoes two major changes:
- The `PowerOfTwo` type is replaced by `Alignment`, which is heavily inspired by the nightly type of the same name in the standard library [3]. - The `last_set_bit` function is dropped, with the recommendation to use the standard library's `checked_ilog2` which does essentially the same thing. The upstream `Alignment` is more constrained than the `PowerOfTwo` of the last revision: it uses `usize` internally instead of a generic value, and does not provide `align_down` or `align_up` methods. These two shortcomings come together very nicely to gift us with a nice headache: we need to align values potentially larger than `usize`, thus need to make `align_down` and `align_up` generic. The generic parameter needs to be constrained on the operations used to perform the alignment (e.g. `BitAnd`, `Not`, etc) and there is one essential operation for which no trait exists in the standard library: `checked_add`. Thus the first patch of this series introduces a trait for it in the `num` module and implements it for all integer types. I suspect we will need something alongside these lines for other purposes anyway, and probably other traits too. This generic nature also restricts these methods to being non-const, unfortunately. I have tried to implement them as macros instead, but quickly hit a wall due to the inability to convert `Alignment`'s `usize` into the type of the value to align. So here it is, not perfect but the need for a standard way to align is starting to become more pressing. [1] https://lore.kernel.org/rust-for-linux/[email protected]/T/#m09e068ecadf5b41099d4c6c55e13fbb3a98c5839 [2] https://github.com/rust-lang/libs-team/issues/631 [3] https://doc.rust-lang.org/std/ptr/struct.Alignment.html Signed-off-by: Alexandre Courbot <[email protected]> --- Changes in v2: - Fix indentation of paste! in impl_last_set_bit. - Link to v1: https://lore.kernel.org/r/[email protected] Changes since split from the nova-core series: - Rename `fls` to `last_set_bit`, - Generate per-type doctests, - Add invariants section to `PowerOfTwo`. - Do not use reference to `self` in `PowerOfTwo` methods since it implements `Copy`, - Use #[derive] where possible instead of implementing traits manually, - Remove `Deref` and `Borrow` implementations. --- Alexandre Courbot (4): rust: add `CheckedAdd` trait rust: add `Alignment` type gpu: nova-core: use Alignment for alignment-related operations gpu: nova-core: use `checked_ilog2` to emulate `fls` Documentation/gpu/nova/core/todo.rst | 15 --- drivers/gpu/nova-core/falcon/hal/ga102.rs | 4 +- drivers/gpu/nova-core/fb.rs | 6 +- drivers/gpu/nova-core/firmware/fwsec.rs | 11 +- drivers/gpu/nova-core/vbios.rs | 4 +- rust/kernel/lib.rs | 2 + rust/kernel/num.rs | 28 ++++ rust/kernel/ptr.rs | 213 ++++++++++++++++++++++++++++++ 8 files changed, 255 insertions(+), 28 deletions(-) --- base-commit: 14ae91a81ec8fa0bc23170d4aa16dd2a20d54105 change-id: 20250620-num-9420281c02c7 Best regards, -- Alexandre Courbot <[email protected]>
