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

[Emil Renner Berthing]

On Tue, 22 Aug 2023 at 05:33, Xingyu Wu <xingyu.wu@xxxxxxxxxxxxxxxx> wrote:
> On 2023/8/21 23:38, Emil Renner Berthing wrote:
> > On Mon, 21 Aug 2023 at 17:29, Xingyu Wu <xingyu.wu@xxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxx>
> >> Fixes: e2c510d6d630 ("riscv: dts: starfive: Add cpu scaling for JH7110 SoC")
> >> Signed-off-by: Xingyu Wu <xingyu.wu@xxxxxxxxxxxxxxxx>
> >> ---
> >>
> >> 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.

Right, but what I'm saying is that if calling clk_set_rate() on the
PLL0 clock causes a crash, that sounds like a bug in the driver. If
you fix that bug, and make clk_set_rate() on the PLL0 clock do the
procedure above when changing the rate, then the PLL0 clock can work
just like any other clock and assigned-clock-rates would work.

/Emil

>
> 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
> >>
>