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    SubjectRe: [PATCH v3 56/65] clk: ingenic: cgu: Switch to determine_rate
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    Hi Maxime,

    Le mardi 04 avril 2023 à 12:11 +0200, Maxime Ripard a écrit :
    > The Ingenic CGU 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().

    As I said in the v2 (IIRC), clk_set_parent() is used when re-parenting
    from the device tree.

    >
    > 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.

    So just to be sure, this patch won't make clk_set_rate() automatically
    switch parents, right?

    Allowing automatic re-parenting sounds like a huge can of worms...

    Cheers,
    -Paul

    >
    > Signed-off-by: Maxime Ripard <maxime@cerno.tech>
    > ---
    >  drivers/clk/ingenic/cgu.c | 15 ++++++++-------
    >  1 file changed, 8 insertions(+), 7 deletions(-)
    >
    > diff --git a/drivers/clk/ingenic/cgu.c b/drivers/clk/ingenic/cgu.c
    > index 1f7ba30f5a1b..0c9c8344ad11 100644
    > --- a/drivers/clk/ingenic/cgu.c
    > +++ b/drivers/clk/ingenic/cgu.c
    > @@ -491,22 +491,23 @@ ingenic_clk_calc_div(struct clk_hw *hw,
    >         return div;
    >  }
    >  
    > -static long
    > -ingenic_clk_round_rate(struct clk_hw *hw, unsigned long req_rate,
    > -                      unsigned long *parent_rate)
    > +static int ingenic_clk_determine_rate(struct clk_hw *hw,
    > +                                     struct clk_rate_request *req)
    >  {
    >         struct ingenic_clk *ingenic_clk = to_ingenic_clk(hw);
    >         const struct ingenic_cgu_clk_info *clk_info =
    > to_clk_info(ingenic_clk);
    >         unsigned int div = 1;
    >  
    >         if (clk_info->type & CGU_CLK_DIV)
    > -               div = ingenic_clk_calc_div(hw, clk_info,
    > *parent_rate, req_rate);
    > +               div = ingenic_clk_calc_div(hw, clk_info, req-
    > >best_parent_rate,
    > +                                          req->rate);
    >         else if (clk_info->type & CGU_CLK_FIXDIV)
    >                 div = clk_info->fixdiv.div;
    >         else if (clk_hw_can_set_rate_parent(hw))
    > -               *parent_rate = req_rate;
    > +               req->best_parent_rate = req->rate;
    >  
    > -       return DIV_ROUND_UP(*parent_rate, div);
    > +       req->rate = DIV_ROUND_UP(req->best_parent_rate, div);
    > +       return 0;
    >  }
    >  
    >  static inline int ingenic_clk_check_stable(struct ingenic_cgu *cgu,
    > @@ -626,7 +627,7 @@ static const struct clk_ops ingenic_clk_ops = {
    >         .set_parent = ingenic_clk_set_parent,
    >  
    >         .recalc_rate = ingenic_clk_recalc_rate,
    > -       .round_rate = ingenic_clk_round_rate,
    > +       .determine_rate = ingenic_clk_determine_rate,
    >         .set_rate = ingenic_clk_set_rate,
    >  
    >         .enable = ingenic_clk_enable,
    >

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