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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 11 Apr 2023 12:27:38 +0200
Message-ID: <CAMuHMdXUEOP_3zjf8nwDyHvZVG-D0AsBjnr=esKzejMMcEiLSQ@mail.gmail.com>
Subject: Re: [PATCH v3 28/65] clk: renesas: r9a06g032: Add a determine_rate hook
To:     Maxime Ripard <maxime@cerno.tech>
Cc:     Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        =?UTF-8?Q?Andreas_F=C3=A4rber?= <afaerber@suse.de>,
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CC Gareth, Hervé, Miquel, Ralph

On Tue, Apr 4, 2023 at 2:44 PM Maxime Ripard <maxime@cerno.tech> wrote:
> The Renesas r9a06g032 bitselect 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().
>
> 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@cerno.tech>

LGTM, so
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
But I do not have the hardware.

> --- a/drivers/clk/renesas/r9a06g032-clocks.c
> +++ b/drivers/clk/renesas/r9a06g032-clocks.c
> @@ -1121,6 +1121,7 @@ static int r9a06g032_clk_mux_set_parent(struct clk_hw *hw, u8 index)
>  }
>
>  static const struct clk_ops clk_bitselect_ops = {
> +       .determine_rate = __clk_mux_determine_rate,
>         .get_parent = r9a06g032_clk_mux_get_parent,
>         .set_parent = r9a06g032_clk_mux_set_parent,
>  };
> @@ -1145,7 +1146,7 @@ r9a06g032_register_bitsel(struct r9a06g032_priv *clocks,
>
>         init.name = desc->name;
>         init.ops = &clk_bitselect_ops;
> -       init.flags = CLK_SET_RATE_PARENT;
> +       init.flags = CLK_SET_RATE_PARENT | CLK_SET_RATE_NO_REPARENT;
>         init.parent_names = names;
>         init.num_parents = 2;
>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds