Hi Boris, > On 3 Feb 2026, at 07:39, Boris Brezillon <[email protected]> > wrote: > > On Mon, 19 Jan 2026 12:35:21 +0000 > Alice Ryhl <[email protected]> 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
The problem with what you have suggested is that the previous state is not consumed if you can clone it, and consuming the previous state is a pretty key element in ensuring you cannot misuse it. For example, here: let enabled_clk = prepared_clk.clone().enable()?; // do stuff // enabled_clk goes out of scope and releases the enable // ref it had prepared_clk is still alive. Now, this may not be the end of the world in this particular case, but for API consistency, I'd say we should probably avoid this behavior. I see that Alice suggested a closure approach. IMHO, we should use that instead. — Daniel
