Re: [PATCH v2 28/65] clk: renesas: r9a06g032: Add a determine_rate hook

[Geert Uytterhoeven <geert@linux-m68k.org>]

CC Gareth

On Fri, Nov 4, 2022 at 2:18 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>
> ---
>  drivers/clk/renesas/r9a06g032-clocks.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/clk/renesas/r9a06g032-clocks.c b/drivers/clk/renesas/r9a06g032-clocks.c
> index 983faa5707b9..70c37097ca6e 100644
> --- a/drivers/clk/renesas/r9a06g032-clocks.c
> +++ b/drivers/clk/renesas/r9a06g032-clocks.c
> @@ -773,6 +773,7 @@ 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,
>  };
> @@ -797,7 +798,7 @@ 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;
>
>
> --
> b4 0.11.0-dev-99e3a