[PATCH 2/3] clk: renesas: rcar-gen4: Add support for fractional multiplication

[Geert Uytterhoeven]

On Thu, Dec 8, 2022 at 2:07 PM Geert Uytterhoeven
<geert+renesas at glider.be> wrote:
> R-Car Gen4 PLLs support fractional multiplication, which can improve
> accuracy when configuring a specific frequency.
>
> Add support for fractional multiplication to the custom clock driver
> for PLLs, which is currently used only for PLL2 on R-Car V4H.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas at glider.be>
> ---
> I am not so sure it is worth supporting this.
> On R-Car V4H, the following clock rates are seen for PLL2 and the
> Cortex-A76 CPU core clock, when using the Normal vs. the
> High-Performance mode:
>
>                                         Multiplication Mode
>                                         Integer         Frational
>                                         ----------      ----------
>     Normal (1.7 GHz):            PLL2   3399999864      3399999997
>                                  Z0     1699999932      1699999999
>     High-Performance (1.8 GHz):  PLL2   3599999856      3599999997
>                                  Z0     1799999928      1799999999
>
> The improvement is of a similar order of magnitude as the accuracy of
> the external crystal, hence insignificant...

Hence I'm ignoring this, unless someone has a good reason to push
through...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at 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