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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Date:   Tue, 22 Aug 2023 11:27:45 +0800
From:   Xingyu Wu <xingyu.wu@...rfivetech.com>
To:     Emil Renner Berthing <emil.renner.berthing@...onical.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 2023/8/21 23:38, Emil Renner Berthing wrote:
> 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

Hi Emil,

The frequency of PLL0 is set according to this process to avoid crash:
1. The divider of the cpu_core clock should be set to 2 if PLL0 is set to 1.5GHz.
2. The parent of cpu_root is changed from pll0 to osc.
3. The PLL0 is set to 1.5GHz.
4. The parent of cpu_root is changed from osc to pll0 back.
I don't think assigned-clock-rates/assigned-clock-parents can do such a complicated job.

Best regards,
Xingyu Wu

> 
>> [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
>>