linux-kernel - Re: [PATCH v2 34/65] clk: ux500: prcmu: Add a determine

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Message-ID: <CACRpkdYwM6X8bBABCisUGX=P4F=hcFb7QLT3Cu7XUWUvV4TE1Q@mail.gmail.com>
Date:   Tue, 8 Nov 2022 14:25:04 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Stephen Boyd <sboyd@...nel.org>,
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Subject: Re: [PATCH v2 34/65] clk: ux500: prcmu: Add a determine_rate hook

On Fri, Nov 4, 2022 at 2:32 PM Maxime Ripard <maxime@...no.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.

So set/get_parent() is never used on clkout.

I think I just added the callbacks for completeness, should we delete them
altogether? The patch is probably fine as-is as well so
Acked-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij