Date:   Wed, 9 Nov 2022 10:43:26 +0800
From:   Chunyan Zhang <zhang.lyra@...il.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Stephen Boyd <sboyd@...nel.org>,
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Subject: Re: [PATCH v2 58/65] clk: sprd: composite: Switch to determine_rate

On Fri, 4 Nov 2022 at 21:33, Maxime Ripard <maxime@...no.tech> wrote:
>
> The Spreadtrum composite clocks 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 driver does implement round_rate() though, which means that we can
> change the rate of the clock, but we will never get to change the
> parent.
>
> However, It's hard to tell whether it's been done on purpose or not.
>
> Since we'll start mandating a determine_rate() implementation, let's
> convert the round_rate() implementation to a determine_rate(), which
> will also make the current behavior explicit. And if it was an
> oversight, the clock behaviour can be adjusted later on.
>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>

Acked-by: Chunyan Zhang <zhang.lyra@...il.com>

Thanks,
Chunyan

> ---
>  drivers/clk/sprd/composite.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/clk/sprd/composite.c b/drivers/clk/sprd/composite.c
> index ebb644820b1e..d3a852720c07 100644
> --- a/drivers/clk/sprd/composite.c
> +++ b/drivers/clk/sprd/composite.c
> @@ -9,13 +9,19 @@
>
>  #include "composite.h"
>
> -static long sprd_comp_round_rate(struct clk_hw *hw, unsigned long rate,
> -                               unsigned long *parent_rate)
> +static int sprd_comp_determine_rate(struct clk_hw *hw,
> +                                   struct clk_rate_request *req)
>  {
>         struct sprd_comp *cc = hw_to_sprd_comp(hw);
> +       unsigned long rate;
>
> -       return sprd_div_helper_round_rate(&cc->common, &cc->div,
> -                                        rate, parent_rate);
> +       rate = sprd_div_helper_round_rate(&cc->common, &cc->div,
> +                                         req->rate, &req->best_parent_rate);
> +       if (rate < 0)
> +               return rate;
> +
> +       req->rate = rate;
> +       return 0;
>  }
>
>  static unsigned long sprd_comp_recalc_rate(struct clk_hw *hw,
> @@ -53,7 +59,7 @@ const struct clk_ops sprd_comp_ops = {
>         .get_parent     = sprd_comp_get_parent,
>         .set_parent     = sprd_comp_set_parent,
>
> -       .round_rate     = sprd_comp_round_rate,
> +       .determine_rate = sprd_comp_determine_rate,
>         .recalc_rate    = sprd_comp_recalc_rate,
>         .set_rate       = sprd_comp_set_rate,
>  };
>
> --
> b4 0.11.0-dev-99e3a

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