Re: [PATCH v2 05/28] clk: renesas: rzg2l: fix computation formula

Geert Uytterhoeven
2023-10-04T08:09:22Z

On Fri, Sep 29, 2023 at 7:39 AM Claudiu <claudiu.beznea@tuxon.dev> wrote:
> From: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>
> According to hardware manual of RZ/G2L (r01uh0914ej0130-rzg2l-rzg2lc.pdf)
> the computation formula for PLL rate is as follows:
>
> Fout = ((m + k/65536) * Fin) / (p * 2^s)
>
> and k has values in range [-32768, 32767]. Dividing k by 65536 with
> integer variables leads all the time to zero. Thus we may have slight
> differences b/w what has been set vs. what is displayed. Thus,
> get rid of this and decompose the formula before dividing k by 65536.
>
> Fixes: ef3c613ccd68a ("clk: renesas: Add CPG core wrapper for RZ/G2L SoC")
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
> ---
>
> Changes in v2:
> - used mul_u64_u32_shr()

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
i.e. will queue in renesas-clk-for-v6.7.

> --- a/drivers/clk/renesas/rzg2l-cpg.c
> +++ b/drivers/clk/renesas/rzg2l-cpg.c
> @@ -695,18 +695,18 @@ static unsigned long rzg2l_cpg_pll_clk_recalc_rate(struct clk_hw *hw,
> struct pll_clk *pll_clk = to_pll(hw);
> struct rzg2l_cpg_priv *priv = pll_clk->priv;
> unsigned int val1, val2;
> - unsigned int mult = 1;
> - unsigned int div = 1;
> + u64 rate;
>
> if (pll_clk->type != CLK_TYPE_SAM_PLL)
> return parent_rate;
>
> val1 = readl(priv->base + GET_REG_SAMPLL_CLK1(pll_clk->conf));
> val2 = readl(priv->base + GET_REG_SAMPLL_CLK2(pll_clk->conf));
> - mult = MDIV(val1) + KDIV(val1) / 65536;
> - div = PDIV(val1) << SDIV(val2);
>
> - return DIV_ROUND_CLOSEST_ULL((u64)parent_rate * mult, div);
> + rate = mul_u64_u32_shr(parent_rate, (MDIV(val1) << 16) + (s16)KDIV(val1),

As KDIV() is always a signed number, I will move the cast to s16 to
the definition of KDIV() while applying.

> + 16 + SDIV(val2));
> +
> + return DIV_ROUND_CLOSEST_ULL(rate, PDIV(val1));
> }
>
> static const struct clk_ops rzg2l_cpg_pll_ops = {

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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