On Wed, Mar 27, 2019 at 01:31:33PM +0100, Geert Uytterhoeven wrote:
> From: Takeshi Kihara <takeshi.kihara...@renesas.com>
>
> 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...@renesas.com>
> Fixes: 90c073e53909da85 ("clk: shmobile: r8a7795: Add SD divider support")
> Signed-off-by: Geert Uytterhoeven <geert+rene...@glider.be>
> ---
> 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?
>
> - 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?
> }
>
> static long cpg_sd_clock_round_rate(struct clk_hw *hw, unsigned long rate,
> @@ -405,13 +410,6 @@ static struct clk * __init cpg_sd_clk_register(const
> char *name,
> val |= CPG_SD_STP_MASK | (clock->div_table[0].val & CPG_SD_FC_MASK);
> writel(val, clock->csn.reg);
>
> - clock->div_max = clock->div_table[0].div;
> - clock->div_min = clock->div_max;
> - for (i = 1; i < clock->div_num; i++) {
> - clock->div_max = max(clock->div_max, clock->div_table[i].div);
> - clock->div_min = min(clock->div_min, clock->div_table[i].div);
> - }
> -
> clk = clk_register(NULL, &clock->hw);
> if (IS_ERR(clk))
> goto free_clock;
> --
> 2.17.1
>
