Re: [PATCH v7 05/10] rust: io: add IoLoc and IoWrite types

[Gary Guo]

On Mon Mar 2, 2026 at 1:12 PM GMT, Danilo Krummrich wrote:
> On Mon Mar 2, 2026 at 1:53 PM CET, Gary Guo wrote:
>> On Mon Mar 2, 2026 at 1:44 AM GMT, Alexandre Courbot wrote:
>>> That should be doable. Note that we currently support `zeroed` and
>>> `default` as initializers, so having the same level of coverage would
>>> require two `write` variants. I'd like to hear what Danilo thinks.
>>
>> I wonder if just providing a single version that starts with
>> `Default::default()` should be sufficient? For most users, zeroed version is the
>> default version anyway. For those where default is not zero, it perhaps makes
>> more sense to start with default anyway; if explicitly zeroing is needed they
>> can always do an explicit `::zeroed()`.
>
> I was thinking about this for a while and also thought that we probably only
> ever need a version that starts with Default::default().
>
> What I still dislike is that the common case becomes write_with() instead of
> just write(). (Just to clarify, the name write_with() is perfectly fine for what
> the function does, it's more that we need it in the first place.)
>
> Also, IIUC, if the value is not created within the closure, we'd still have the
> following redundancy, right?
>
> 	let reg = regs::NV_PFALCON_FALCON_DMATRFMOFFS::of::<E>()
> 		.try_init(|r| r.try_with_offs(load_offsets.dst_start + pos))?;
>
> 	bar.write(regs::NV_PFALCON_FALCON_DMATRFMOFFS::of::<E>(), reg);
>
> It's just that this case nicely converts to write_with().

You would have

    let reg = regs::NV_PFALCON_FALCON_DMATRFMOFFS::default()
        .try_with_offs(load_offsets.dst_start + pos))?;

    bar.write(regs::NV_PFALCON_FALCON_DMATRFMOFFS::of::<E>(), reg);

Note that the `default()` invocation doesn't mention relative base, as it's just
plain bitfields without offset at that point. [ I like the fact that this
doesn't need to use closure, as I generally prefer code without them, perhaps I
am not "rusty" enough :) ]

In my view, if the code is complex enough that you have

    let reg = ...;
    <some code>
    bar.write(reg)

then it probably makes sense to have register name mentioned again (this is
typed checked anyway so you don't need to worry about misnaming it). Otherwise,
one might read the code and be confused about what register is being written to
at all.

I think for explicit location parameter makes much more sense for relative
addressed registers and register arrays.

Best,
Gary