Re: [PATCH v8 06/10] rust: io: use generic read/write accessors for primitive accesses

["Alexandre Courbot" <acourbot@nvidia.com>]

On Tue Mar 10, 2026 at 10:57 AM JST, Alexandre Courbot wrote:
> On Tue Mar 10, 2026 at 12:29 AM JST, Gary Guo wrote:
>> On Mon Mar 9, 2026 at 3:14 PM GMT, Alexandre Courbot wrote:
>>> By providing the required `IoLoc` implementations on `usize`, we can
>>> leverage the generic accessors and reduce the number of unsafe blocks in
>>> the module.
>>>
>>> This also allows us to directly call the generic `read/write/update`
>>> methods with primitive types, so add examples illustrating this.
>>>
>>> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
>>> ---
>>>  rust/kernel/io.rs | 199 +++++++++++++++++++++++++++++++++++-------------------
>>>  1 file changed, 131 insertions(+), 68 deletions(-)
>>>
>>> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
>>> index 1db6572f4a42..ed6fab001a39 100644
>>> --- a/rust/kernel/io.rs
>>> +++ b/rust/kernel/io.rs
>>> @@ -197,6 +197,25 @@ pub trait IoLoc<T> {
>>>      fn offset(&self) -> usize;
>>>  }
>>>  
>>> +/// Implements [`IoLoc<$ty>`] for [`usize`], allowing to use `usize` as a parameter of
>>> +/// [`Io::read`] and [`Io::write`].
>>> +macro_rules! impl_usize_ioloc {
>>> +    ($($ty:ty),*) => {
>>> +        $(
>>> +            impl IoLoc<$ty> for usize {
>>> +                type IoType = $ty;
>>> +
>>
>> #[inline(always)]
>>
>> the fact that this is a pointer is somewhat uneasy to me. I wonder if Clippy
>> with its inlining tweak would cause optimisation failure here.
>>
>> Could this be just `fn offset(self)`?
>
> Yes, this was a remnant from a previous design where I needed to either
> make `IoLoc` require `Copy` or use a reference here, so I opted for the
> latter.
>
> With the current code though we are using `IoLoc`s exactly one time, so
> we can consume `self` without requiring `Copy`.

I also guess this method should be renamed `into_offset` then?