Hi Simon,
On Fri, Mar 29, 2019 at 9:45 AM Simon Horman <horms@xxxxxxxxxxxx> wrote:
> On Wed, Mar 27, 2019 at 01:31:33PM +0100, Geert Uytterhoeven wrote:
> > From: Takeshi Kihara <takeshi.kihara.df@xxxxxxxxxxx>
> >
> > cpg_sd_clock_round_rate() may return an unsupported clock rate for the
> > requested clock rate. Therefore, when cpg_sd_clock_set_rate() sets the
> > clock rate acquired by cpg_sd_clock_round_rate(), an error may occur.
> >
> > This is not conform the clk API design.
> >
> > This patch fixes that by making sure cpg_sd_clock_calc_div() considers
> > only the division values defined in cpg_sd_div_table[].
> > With this fix, the cpg_sd_clock_round_rate() always return a support
> > clock rate.
> >
> > Signed-off-by: Takeshi Kihara <takeshi.kihara.df@xxxxxxxxxxx>
> > Fixes: 90c073e53909da85 ("clk: shmobile: r8a7795: Add SD divider support")
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> > ---
> > To be queued in clk-renesas-for-v5.2.
> >
> > drivers/clk/renesas/rcar-gen3-cpg.c | 28 +++++++++++++---------------
> > 1 file changed, 13 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/clk/renesas/rcar-gen3-cpg.c b/drivers/clk/renesas/rcar-gen3-cpg.c
> > index d5fb768b089ff1c1..d2745c57207efc01 100644
> > --- a/drivers/clk/renesas/rcar-gen3-cpg.c
> > +++ b/drivers/clk/renesas/rcar-gen3-cpg.c
> > @@ -3,6 +3,7 @@
> > * R-Car Gen3 Clock Pulse Generator
> > *
> > * Copyright (C) 2015-2018 Glider bvba
> > + * Copyright (C) 2019 Renesas Electronics Corp.
> > *
> > * Based on clk-rcar-gen3.c
> > *
> > @@ -236,8 +237,6 @@ struct sd_clock {
> > const struct sd_div_table *div_table;
> > struct cpg_simple_notifier csn;
> > unsigned int div_num;
> > - unsigned int div_min;
> > - unsigned int div_max;
> > unsigned int cur_div_idx;
> > };
> >
> > @@ -314,14 +313,20 @@ static unsigned int cpg_sd_clock_calc_div(struct sd_clock *clock,
> > unsigned long rate,
> > unsigned long parent_rate)
> > {
> > - unsigned int div;
> > -
> > - if (!rate)
> > - rate = 1;
> > + unsigned long calc_rate, best_rate = 0, diff, diff_min = ULONG_MAX;
> > + unsigned int i;
> >
> > - div = DIV_ROUND_CLOSEST(parent_rate, rate);
> > + for (i = 0; i < clock->div_num; i++) {
> > + calc_rate = DIV_ROUND_CLOSEST(parent_rate,
> > + clock->div_table[i].div);
> > + diff = calc_rate > rate ? calc_rate - rate : rate - calc_rate;
> > + if (diff <= diff_min) {
> > + best_rate = calc_rate;
> > + diff_min = diff;
> > + }
> > + }
>
> My reading is that.
> a) this algorithm picks a clock based on the div field of the
> members of cpg_sd_div_table. and
> b) in the case of duplicate values of that field the first one is chosen; and
> c) such duplicates (of sd_div values) do exist in cpg_sd_div_table
>
> Is this the intended behaviour?
Actually cpg_sd_clock_calc_div() picks the last one, due to the "<=" :-)
But that doesn't matter here, as both dividers are equal.
cpg_sd_clock_set_rate() will pick the first entry from the table with matching
div value later.
> > - return clamp_t(unsigned int, div, clock->div_min, clock->div_max);
> > + return DIV_ROUND_CLOSEST(parent_rate, best_rate);
>
> Would it be better to return the value of clock->div_table[i].div
> that yielded best_rate?
True. The DIV_ROUND_CLOSEST() is not needed, as we could have
saved best_div instead of best_rate. Will fix.
Thanks!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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
