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

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

On Tue, 3 Feb 2026 12:26:31 +0100
Boris Brezillon <boris.brezillon@collabora.com> wrote:

> On Tue, 3 Feb 2026 11:39:02 +0100
> Boris Brezillon <boris.brezillon@collabora.com> wrote:
> 
> > 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]  
> 
> This time with a proper RawClk(*mut bindings::clk) wrapper, so we can
> clk_put() called in RawClk::drop() instead of in Clk::drop().
> 
> [1]https://gitlab.freedesktop.org/bbrezillon/linux/-/commit/6fa6cb72f14373b276c61d038bc2b16f49c78f74

And I forgot to drop the ManuallyDrop in that one, but I bet you get the
idea.