Re: [PATCH v1] rust: serdev: use Delta<Jiffy> for timeouts

["Gary Guo" <gary@garyguo.net>]

On Thu Oct 1, 2026 at 2:28 AM BST, FUJITA Tomonori wrote:
> On Thu, 01 Oct 2026 01:39:51 +0100
> "Gary Guo" <gary@garyguo.net> wrote:
>
>> On Thu Oct 1, 2026 at 1:29 AM BST, FUJITA Tomonori wrote:
>>> On Wed, 30 Sep 2026 14:52:50 +0100
>>> "Gary Guo" <gary@garyguo.net> wrote:
>>>
>>>> I think the API should ideally use `Option<Delta<Jiffies>>` for this case, and
>>>> use `None` to represent indefinite wait.
>>>
>>> For read_poll_timeout(), where a timeout of 0 means "never time out"
>>> in C, we did not take Option for the timeout. Alice's comment [1]:
>>>
>>> | Another thing is the `timeout_delta` option. I would just have
>>> | written it as two methods, one that takes a timeout and one that
>>> | doesn't. That way, callers that don't need a timeout do not need to
>>> | handle timeout errors. (Do we have any users without a timeout? If
>>> | not, maybe just remove the Option.)
>>>
>>> serdev is in the same situation. Do we want an API that uses None for
>>> "never" here?
>> 
>> I don't like the "using 0" to mean forever, because 0 has a more sensible
>> meaning -- which is just do a poll and don't wait.
>
> Fully agreed.
>
>> This one doesn't even return a result at all, so `Option` sounds reasonable.
>
> That's true for wait_until_sent(), but write_all() returns a result
> and it can be ETIMEDOUT.
>
>> Alternatively, just use `MAX_SCHEDULE_TIMEOUT` (i.e.
>> `Delta::from_jiffies(isize::MAX)`). We can perhaps add a `Delta::MAX` for this.
>
> I don't think Delta::<Jiffy>::MAX is a good idea. Whether the maximum
> value means an indefinite wait depends on the function. For example,
> it doesn't for Queue::enqueue_delayed().

Whether it means infinite or not depends on the function, but that's still mean
"MAX", no?

Also, it's not like serdev_device_wait_until_sent use it to mean infinite
either. I randomly sampled two wait_until_sent impls and they just use the
timeout in arithmetic, so it's just a very long wait.

Best,
Gary