linux-kernel - Re: [PATCH v3] clk: renesas: r8a774c0: Add RPC clocks

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Message-ID: <CAMuHMdUky4OEvCLnDYr3C-PB+PKdSx3U5+dCfhiftDhf3RKmAQ@mail.gmail.com>
Date:   Mon, 16 Nov 2020 09:33:59 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Biju Das <biju.das.jz@...renesas.com>,
        Prabhakar <prabhakar.csengg@...il.com>
Subject: Re: [PATCH v3] clk: renesas: r8a774c0: Add RPC clocks

Hi Prabhakar,

On Tue, Nov 10, 2020 at 1:56 PM Lad Prabhakar
<prabhakar.mahadev-lad.rj@...renesas.com> wrote:
> Describe the RPCSRC internal clock and the RPC[D2] clocks derived from it,
> as well as the RPC-IF module clock, in the RZ/G2E (R8A774C0) CPG/MSSR
> driver.
>
> Add new clk type CLK_TYPE_GEN3E3_RPCSRC to register rpcsrc as a fixed
> clock on R-Car Gen3 E3 (and also RZ/G2E which is identical to E3 SoC),
> parent and the divider is set based on the register value CPG_RPCCKCR[4:3]
> (parent is cross verified against MD[4:1] pins) which has been set prior
> to booting the kernel.
>
> MD[4] MD[3] MD[2] MD[1]
>   0     0     0    1     -> RPCSRC CLK source is PLL1
>   0     0     1    1     -> RPCSRC CLK source is PLL1
>   0     1     0    0     -> RPCSRC CLK source is PLL1
>   1     0     1    1     -> RPCSRC CLK source is PLL1
>   x     x     x    x     -> For any other values RPCSRC CLK source is PLL0
>
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> Reviewed-by: Biju Das <biju.das.jz@...renesas.com>

Thanks for your patch!

> ---
> v2->v3
> * Implemented as a fixed clock

Sounds fine to me.  If we ever need to configure this clock from Linux,
the driver can be changed.

> --- a/drivers/clk/renesas/rcar-gen3-cpg.c
> +++ b/drivers/clk/renesas/rcar-gen3-cpg.c
> @@ -427,6 +427,19 @@ static struct clk * __init cpg_sd_clk_register(const char *name,
>         return clk;
>  }
>
> +static bool __init cpg_rpcsrc_e3_parent_is_pll0(u32 mode)
> +{
> +       unsigned int e3_rpcsrc = (mode & GENMASK(4, 1)) >> 1;
> +       unsigned int pll1[] = { 0x1, 0x3, 0x4, 0xb, };
> +       int i;
> +
> +       for (i = 0; i < ARRAY_SIZE(pll1); i++)
> +               if (e3_rpcsrc == pll1[i])
> +                       return false;

Did you know gcc (version 9.3.0) generates smaller code for:

        switch (e3_rpcsrc) {
        case 0x1:
        case 0x3:
        case 0x4:
        case 0xb:
                return false;

        default:
                return true;
        }

?

> @@ -696,6 +709,42 @@ struct clk * __init rcar_gen3_cpg_clk_register(struct device *dev,
>                                                   cpg_rpcsrc_div_table,
>                                                   &cpg_lock);
>
> +       case CLK_TYPE_GEN3E3_RPCSRC:
> +               /*
> +                * Register RPCSRC as fixed factor clock based on the
> +                * MD[4:1] pins and CPG_RPCCKCR[4:3] register value for
> +                * which has been set prior to booting the kernel.
> +                */
> +
> +               value = (readl(base + CPG_RPCCKCR) & GENMASK(4, 3)) >> 3;
> +               if (cpg_rpcsrc_e3_parent_is_pll0(cpg_mode)) {
> +                       if (value != 2)
> +                               return ERR_PTR(-EINVAL);
> +               } else {
> +                       if (value == 2)
> +                               return ERR_PTR(-EINVAL);
> +               }

IMHO this cross-verification is not needed, and harmful: it prevents the
boot loader from changing the configuration, which I think is a valid
use case.

> +
> +               switch (value) {
> +               case 0:
> +                       div = 5;
> +                       break;
> +               case 1:
> +                       div = 3;
> +                       break;
> +               case 2:
> +                       parent = clks[core->parent >> 16];
> +                       if (IS_ERR(parent))
> +                               return ERR_CAST(parent);
> +                       div = 8;

R-Car D3 is very similar, but uses div = 5 instead of 8.
Perhaps this value can be retrieved from cpg_core_clk.div?
Of course, we can do that later, when D3 support is added.

> +                       break;
> +               case 3:
> +               default:
> +                       div = 2;
> +                       break;
> +               }
> +               break;
> +
>         case CLK_TYPE_GEN3_RPC:
>                 return cpg_rpc_clk_register(core->name, base,
>                                             __clk_get_name(parent), notifiers);

The rest looks good to me.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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