Re: [PATCH v2 34/65] clk: ux500: prcmu: Add a determine_rate hook

Maxime Ripard
2022-11-09T11:06:05Z

Hi Linus,

On Tue, Nov 08, 2022 at 02:25:04PM +0100, Linus Walleij wrote:
> On Fri, Nov 4, 2022 at 2:32 PM Maxime Ripard <maxime@cerno.tech> wrote:
>
> > The UX500 PRCMU "clkout" clock implements a mux with a set_parent hook,
> > but doesn't provide a determine_rate implementation.
> >
> > This is a bit odd, since set_parent() is there to, as its name implies,
> > change the parent of a clock. However, the most likely candidate to
> > trigger that parent change is a call to clk_set_rate(), with
> > determine_rate() figuring out which parent is the best suited for a
> > given rate.
> >
> > The other trigger would be a call to clk_set_parent(), but it's far less
> > used, and it doesn't look like there's any obvious user for that clock.
> >
> > So, the set_parent hook is effectively unused, possibly because of an
> > oversight. However, it could also be an explicit decision by the
> > original author to avoid any reparenting but through an explicit call to
> > clk_set_parent().
>
> It is actually set up from the device tree, typically like this:
>
> /* clkout1 from ACLK divided by 8 */
> clocks = <&clkout_clk DB8500_CLKOUT_1 DB8500_CLKOUT_SRC_ACLK 8>;
>
> So the parent (source) and divisor comes in there.
>
> clk->source and clk->divider is already set up when clk_hw_register() is
> called.

I wasn't aware that we had such bindings. AFAIUI, it looks redundant
with assigned-clock-rates and assigned-clock-parents, could we deprecate
it?

> So set/get_parent() is never used on clkout.
>
> I think I just added the callbacks for completeness, should we delete them
> altogether?

I can't really test any of these platforms, so I'm a bit wary of making
such changes myself. Feel free to send a follow-up if you think it's
needed :)

> The patch is probably fine as-is as well so
> Acked-by: Linus Walleij <linus.walleij@linaro.org>

Thanks!
Maxime