On Mon Jun 15, 2026 at 3:52 PM BST, Alexandre Courbot wrote:
> On Fri Jun 12, 2026 at 1:28 AM JST, Gary Guo wrote:
> <...>
>> +/// A view of memory-mapped I/O region.
>> +///
>> +/// # Invariant
>> +///
>> +/// `ptr` points to a valid and aligned memory-mapped I/O region for the
>> duration lifetime `'a`.
>> +pub struct Mmio<'a, T: ?Sized> {
>> + ptr: *mut T,
>> + phantom: PhantomData<&'a ()>,
>> +}
>> +
>> +impl<T: ?Sized> Copy for Mmio<'_, T> {}
>> +impl<T: ?Sized> Clone for Mmio<'_, T> {
>> + #[inline]
>> + fn clone(&self) -> Self {
>> + *self
>> + }
>> +}
>> +
>> +impl<'a, T: ?Sized> Mmio<'a, T> {
>> + /// Create a `Mmio`, providing the accessors to the MMIO mapping.
>> + ///
>> + /// # Safety
>> + ///
>> + /// `raw` represents an valid and aligned memory-mapped I/O region
>> while `'a` is alive.
>
> typo: "a valid".
>
> <...>
>> -/// [`MmioOwned`] wrapper using relaxed accessors.
>> +/// [`Mmio`] but using relaxed accessors.
>> ///
>> /// This type provides an implementation of [`Io`] that uses relaxed I/O
>> MMIO operands instead of
>> /// the regular ones.
>> ///
>> -/// See [`MmioOwned::relaxed`] for a usage example.
>> -#[repr(transparent)]
>> -pub struct RelaxedMmio<const SIZE: usize = 0>(MmioOwned<SIZE>);
>> +/// See [`Mmio::relaxed`] for a usage example.
>> +///
>> +/// # Invariant
>> +///
>> +/// `ptr` points to a valid and aligned memory-mapped I/O region for the
>> duration lifetime `'a`.
>> +pub struct RelaxedMmio<'a, T: ?Sized> {
>> + ptr: *mut T,
>> + phantom: PhantomData<&'a ()>,
>> +}
>
> Is there a reason for not just declaring `RelaxedMmio` as
>
> #[repr(transparent)]
> pub struct RelaxedMmio<'a, T: ?Sized>(Mmio<'a, T>);
>
> similarly to what the original code did with `MmioOwned`?
>
> I tried locally and could build. This avoids declaring `Mmio` and
> `RelaxedMmio` as basically identical types, and lets us remove the
> explicit `Send` and `Sync` implementations. IIUC you can also reduce or
> even remove the invariant section as it is enforced by `Mmio`.
This is what I did originally, but this would cause duplication for
RelaxedMmioBackend, as now you have to do
unsafe { bindings::$read_fn(view.0.ptr.cast_const().cast()) }
and the `.0` causes the macro not being shared with MmioBackend.
Best,
Gary
