linux-kernel - Re: [PATCH v2] clk: starfive: jh7110-sys: Fix lower rate of CPUfreq by setting PLL0 rate to 1.5GHz

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Message-ID: <CAJM55Z_XxHeC-X2d4qcsRK6THLyqWV4SsSW3S+cC8yszpPD9Og@mail.gmail.com>
Date:   Mon, 21 Aug 2023 17:38:07 +0200
From:   Emil Renner Berthing <emil.renner.berthing@...onical.com>
To:     Xingyu Wu <xingyu.wu@...rfivetech.com>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Conor Dooley <conor@...nel.org>,
        Hal Feng <hal.feng@...rfivetech.com>,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH v2] clk: starfive: jh7110-sys: Fix lower rate of CPUfreq
 by setting PLL0 rate to 1.5GHz

On Mon, 21 Aug 2023 at 17:29, Xingyu Wu <xingyu.wu@...rfivetech.com> wrote:
>
> CPUfreq supports 4 cpu frequency loads on 375/500/750/1500MHz.
> But now PLL0 rate is 1GHz and the cpu frequency loads become
> 333/500/500/1000MHz in fact.
>
> So PLL0 rate should be set to 1.5GHz. Change the parent of cpu_root clock
> and the divider of cpu_core before the setting.
>
> Reviewed-by: Hal Feng <hal.feng@...rfivetech.com>
> Fixes: e2c510d6d630 ("riscv: dts: starfive: Add cpu scaling for JH7110 SoC")
> Signed-off-by: Xingyu Wu <xingyu.wu@...rfivetech.com>
> ---
>
> Hi Stephen and Emil,
>
> This patch fixes the issue about lower rate of CPUfreq[1]
> and sets PLL0 rate to 1.5GHz. In order not to affect the cpu
> operation, the cpu_root's parent clock should be changed first.
> And the divider of the cpu_core clock should be set to 2 so they
> won't crash when setting 1.5GHz without voltage regulation.

Hi Xingyu,

It sounds like this is something the driver should handle
automatically whenever clk_set_rate() is called on the PLL0 clock.
Then we should be able to use regular assigned-clocks /
assigned-clock-rates stanzas in the device tree instead of having this
1.5GHz rate hard-coded in the driver.

/Emil

> [1]: https://github.com/starfive-tech/VisionFive2/issues/55
>
> This patch is based on linux-next(20230818) which has merge PLL driver
> on the StarFive JH7110 SoC.
>
> Thanks,
> Xingyu Wu
>
> ---
>  .../clk/starfive/clk-starfive-jh7110-sys.c    | 47 ++++++++++++++++++-
>  1 file changed, 46 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/clk/starfive/clk-starfive-jh7110-sys.c b/drivers/clk/starfive/clk-starfive-jh7110-sys.c
> index 3884eff9fe93..b6b9e967dfc7 100644
> --- a/drivers/clk/starfive/clk-starfive-jh7110-sys.c
> +++ b/drivers/clk/starfive/clk-starfive-jh7110-sys.c
> @@ -501,7 +501,52 @@ static int __init jh7110_syscrg_probe(struct platform_device *pdev)
>         if (ret)
>                 return ret;
>
> -       return jh7110_reset_controller_register(priv, "rst-sys", 0);
> +       ret = jh7110_reset_controller_register(priv, "rst-sys", 0);
> +       if (ret)
> +               return ret;
> +
> +       /*
> +        * Set PLL0 rate to 1.5GHz
> +        * In order to not affect the cpu when the PLL0 rate is changing,
> +        * we need to switch the parent of cpu_root clock to osc clock first,
> +        * and then switch back after setting the PLL0 rate.
> +        */
> +       pllclk = clk_get(priv->dev, "pll0_out");
> +       if (!IS_ERR(pllclk)) {
> +               struct clk *osc = clk_get(&pdev->dev, "osc");
> +               struct clk *cpu_root = priv->reg[JH7110_SYSCLK_CPU_ROOT].hw.clk;
> +               struct clk *cpu_core = priv->reg[JH7110_SYSCLK_CPU_CORE].hw.clk;
> +
> +               if (IS_ERR(osc)) {
> +                       clk_put(pllclk);
> +                       return PTR_ERR(osc);
> +               }
> +
> +               /*
> +                * CPU need voltage regulation by CPUfreq if set 1.5GHz.
> +                * So in this driver, cpu_core need to be set the divider to be 2 first
> +                * and will be 750M after setting parent.
> +                */
> +               ret = clk_set_rate(cpu_core, clk_get_rate(cpu_core) / 2);
> +               if (ret)
> +                       goto failed_set;
> +
> +               ret = clk_set_parent(cpu_root, osc);
> +               if (ret)
> +                       goto failed_set;
> +
> +               ret = clk_set_rate(pllclk, 1500000000);
> +               if (ret)
> +                       goto failed_set;
> +
> +               ret = clk_set_parent(cpu_root, pllclk);
> +
> +failed_set:
> +               clk_put(pllclk);
> +               clk_put(osc);
> +       }
> +
> +       return ret;
>  }
>
>  static const struct of_device_id jh7110_syscrg_match[] = {
> --
> 2.25.1
>