Re: [PATCH v6 5/9] rust: io: add IoRef and IoWrite types

[Alice Ryhl <aliceryhl@google.com>]

On Fri, Feb 20, 2026 at 03:38:46PM +0900, Alexandre Courbot wrote:
> On Mon Feb 16, 2026 at 7:52 PM JST, Alexandre Courbot wrote:
> > On Mon Feb 16, 2026 at 7:35 PM JST, Alice Ryhl wrote:
> >> On Mon, Feb 16, 2026 at 06:36:29PM +0900, Alexandre Courbot wrote:
> >>> On Mon Feb 16, 2026 at 6:01 PM JST, Alice Ryhl wrote:
> >>> > On Mon, Feb 16, 2026 at 05:04:41PM +0900, Alexandre Courbot wrote:
> >>> >> I/O accesses are defined by the following properties:
> >>> >> 
> >>> >> - For reads, a start address, a width, and a type to interpret the read
> >>> >>   value as,
> >>> >> - For writes, the same as above, and a value to write.
> >>> >> 
> >>> >> Introduce the `IoRef` trait, which allows implementing types to specify
> >>> >> the address a type expects to be accessed at, as well as the width of
> >>> >> the access, and the user-facing type used to perform the access.
> >>> >> 
> >>> >> This allows read operations to be made generic with the `read` method
> >>> >> over an `IoRef` argument.
> >>> >> 
> >>> >> Write operations need a value to write on top of the `IoRef`: fulfill
> >>> >> that purpose with the `IoWrite`, which is the combination of an `IoRef`
> >>> >> and a value of the type it expects. This allows write operations to be
> >>> >> made generic with the `write` method over a single `IoWrite` argument.
> >>> >> 
> >>> >> The main purpose of these new entities is to allow register types to be
> >>> >> written using these generic `read` and `write` methods of `Io`.
> >>> >> 
> >>> >> Co-developed-by: Gary Guo <gary@garyguo.net>
> >>> >> Signed-off-by: Gary Guo <gary@garyguo.net>
> >>> >> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> >>> >> ---
> >>> >>  rust/kernel/io.rs | 243 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >>> >>  1 file changed, 243 insertions(+)
> >>> >> 
> >>> >> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
> >>> >> index b150743ffa4f..6da8593f7858 100644
> >>> >> --- a/rust/kernel/io.rs
> >>> >> +++ b/rust/kernel/io.rs
> >>> >> @@ -173,6 +173,160 @@ pub trait IoCapable<T> {
> >>> >>      unsafe fn io_write(&self, value: T, address: usize);
> >>> >>  }
> >>> >>  
> >>> >> +/// Reference to an I/O location, describing the offset, width, and return type of an access.
> >>> >
> >>> > In the next patch you implement this for usize, but here you say it's a
> >>> > reference to an I/O location. I'm pretty sure usize is not a reference
> >>> > to an I/O location.
> >>> 
> >>> Methods like `read_u8` use a `usize` to reference the location we want
> >>> to read, so aren't they in that context?
> >>
> >> Oh .. I wouldn't use the word "reference" like that. How about "index"
> >> instead?
> >
> > "index" looks more accurate indeed for something that is not a pointer
> > type.
> 
> Actually this creates a bit of confusion in `register.rs`, where we have
> arrays of registers, which `RegisterArrayRef` was built using the index
> of a particular register within that array. If we rename `IoRef` to
> `IoIndex` and transitively `RegisterArrayRef` to `RegisterArrayIndex`,
> we now have an index that takes an index...
> 
> Besides `IoRef` is more than just an index - it is also an access width,
> and a type to convert that access from/to. Would `IoSpec` and
> `specification` be acceptable?

Not using "index" make sense to me, but I don't really understand how
"spec" fits in either. How about "place" or "location"?

Alice