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

[Alexandre Courbot]

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@xxxxxxxxxxx>
>>> >> Signed-off-by: Gary Guo <gary@xxxxxxxxxxx>
>>> >> Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
>>> >> ---
>>> >>  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?