linux-kernel - Re: [PATCH v2 35/65] clk: ux500: sysctrl: Add a determine

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Message-ID: <CACRpkdaOM=T1pRJNK6hdc76m5tQfrjvF9nVBp7ZDf3wOMNSwyg@mail.gmail.com>
Date:   Tue, 8 Nov 2022 14:27:06 +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 35/65] clk: ux500: sysctrl: Add a determine_rate hook

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

> The UX500 sysctrl "set_parent" clocks implement 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().
>
> The latter case would be equivalent to setting the flag
> CLK_SET_RATE_NO_REPARENT, together with setting our determine_rate hook
> to __clk_mux_determine_rate(). Indeed, if no determine_rate
> implementation is provided, clk_round_rate() (through
> clk_core_round_rate_nolock()) will call itself on the parent if
> CLK_SET_RATE_PARENT is set, and will not change the clock rate
> otherwise. __clk_mux_determine_rate() has the exact same behavior when
> CLK_SET_RATE_NO_REPARENT is set.
>
> And if it was an oversight, then we are at least explicit about our
> behavior now and it can be further refined down the line.
>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>

Acked-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij