Re: [PATCH v3 1/3] rust: clk: use the type-state pattern

[Boris Brezillon <boris.brezillon@collabora.com>]

On Mon, 19 Jan 2026 12:35:21 +0000
Alice Ryhl <aliceryhl@google.com> wrote:

> On Mon, Jan 19, 2026 at 11:45:57AM +0100, Maxime Ripard wrote:
> > On Thu, Jan 08, 2026 at 11:14:37AM -0300, Daniel Almeida wrote:  
> > > > For example, it's quite typical to have (at least) one clock for the bus
> > > > interface that drives the register, and one that drives the main
> > > > component logic. The former needs to be enabled only when you're
> > > > accessing the registers (and can be abstracted with
> > > > regmap_mmio_attach_clk for example), and the latter needs to be enabled
> > > > only when the device actually starts operating.
> > > > 
> > > > You have a similar thing for the prepare vs enable thing. The difference
> > > > between the two is that enable can be called into atomic context but
> > > > prepare can't.
> > > > 
> > > > So for drivers that would care about this, you would create your device
> > > > with an unprepared clock, and then at various times during the driver
> > > > lifetime, you would mutate that state.  
> 
> The case where you're doing it only while accessing registers is
> interesting, because that means the Enable bit may be owned by a local
> variable. We may imagine an:
> 
>     let enabled = self.prepared_clk.enable_scoped();
>     ... use registers
>     drop(enabled);
> 
> Now ... this doesn't quite work with the current API - the current
> Enabled stated owns both a prepare and enable count, but the above keeps
> the prepare count in `self` and the enabled count in a local variable.
> But it could be done with a fourth state, or by a closure method:
> 
>     self.prepared_clk.with_enabled(|| {
>         ... use registers
>     });
> 
> All of this would work with an immutable variable of type Clk<Prepared>.

Hm, maybe it'd make sense to implement Clone so we can have a temporary
clk variable that has its own prepare/enable refs and releases them
as it goes out of scope. This implies wrapping *mut bindings::clk in an
Arc<> because bindings::clk is not ARef, but should be relatively easy
to do. Posting the quick experiment I did with this approach, in case
you're interested [1]

[1]https://gitlab.freedesktop.org/bbrezillon/linux/-/commit/d5d04da4f4f6192b6e6760d5f861c69596c7d837