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

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

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?