Re: [PATCH v3] rust: regulator: add a bare minimum regulator abstraction

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

On Sun May 18, 2025 at 11:05 PM JST, Benno Lossin wrote:
> On Sun May 18, 2025 at 1:12 PM CEST, Alexandre Courbot wrote:
>> On Sun May 18, 2025 at 6:57 PM JST, Benno Lossin wrote:
>>> So just let users ensure that they always match each `enable` call with
>>> a `disable` call in the `Dynamic` typestate?
>>>
>>> That is ok, if no memory issues can arise from forgetting to do so,
>>> otherwise those functions need to be `unsafe`.
>>
>> There shouldn't be any, the only side effect would be that the regulator
>> stays enabled when it shouldn't.
>>
>> It's also easy to implement more behaviors using more states. For
>> instance, `Dynamic` just proxies the C API. But if we also think it its
>> useful to have a regulator which use count is clamped to 0 and 1, you
>> could have another state that includes a boolean (instead of being empty
>> lke the others) to track whether the regulator is enabled or not, and an
>> `enable` method that only calls the C `regulator_enable` if that boolean
>> is not already true. That way you remove the need to mirror the calls to
>> enable and disable, while only paying the memory overhead for doing so
>> when you explicitly state you want this behavior.
>
> Aren't we then duplicating the refcount from the C side?

Not exactly, we are just tracking whether the consumer has already
called `regulator_enable` or not. Unfortunately `regulator_is_enabled`
appears to track the enabled state of the regulator device (not the
consumer reference), so it cannot be used for that.

Maybe a better way would be to have a Rust helper that returns the
`enable_count` of the regulator and check that instead. And to be clear
I am not saying this one is the policy we should follow - I just want to
illustrate the fact that the typestate pattern allows us to implement
different kinds of behaviors.