linux-kernel - RE: [PATCH v5 2/2] riscv: dts: starfive: visionfive-2: Fix lower rate of CPUfreq by setting PLL0 rate to 1.5GHz

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Date: Tue, 14 May 2024 07:40:18 +0000
From: Xingyu Wu <xingyu.wu@...rfivetech.com>
To: Samuel Holland <samuel.holland@...ive.com>, Michael Turquette
	<mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, Conor Dooley
	<conor@...nel.org>, Emil Renner Berthing
	<emil.renner.berthing@...onical.com>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
CC: Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
	<palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Hal Feng
	<hal.feng@...rfivetech.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-clk@...r.kernel.org"
	<linux-clk@...r.kernel.org>, "linux-riscv@...ts.infradead.org"
	<linux-riscv@...ts.infradead.org>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>
Subject: RE: [PATCH v5 2/2] riscv: dts: starfive: visionfive-2: Fix lower rate
 of CPUfreq by setting PLL0 rate to 1.5GHz

On 12/05/2024 02:47, Samuel Holland wrote:
> 
> On 2024-05-07 1:53 AM, Xingyu Wu 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.
> >
> > The PLL0 rate should be default set to 1.5GHz and set the cpu_core
> > rate to 500MHz in safe.
> 	
> Can this be accomplished by instead setting the CLK_SET_RATE_PARENT flag on
> the CPU_CORE clock? That way PLL0 is automatically set when cpufreq tries to
> change the CPU core frequency. Then there is no DT change and no compatibility
> issue.
> 
> Regards,
> Samuel

Thanks for your advice. But cpufreq tries to change the CPU core rate and also
the PLL0 rate with the flag of CLK_SET_RATE_PARENT and the PLL0 will be
changed frequently. I think it goes against our intention and the PLL0 rate should
be fixed or rarely changed. This helps to stabilize the system.

Best regards,
Xingyu Wu

> 
> > Fixes: e2c510d6d630 ("riscv: dts: starfive: Add cpu scaling for JH7110
> > SoC")
> > Signed-off-by: Xingyu Wu <xingyu.wu@...rfivetech.com>
> > ---
> >  .../boot/dts/starfive/jh7110-starfive-visionfive-2.dtsi     | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git
> > a/arch/riscv/boot/dts/starfive/jh7110-starfive-visionfive-2.dtsi
> > b/arch/riscv/boot/dts/starfive/jh7110-starfive-visionfive-2.dtsi
> > index 45b58b6f3df8..28981b267de4 100644
> > --- a/arch/riscv/boot/dts/starfive/jh7110-starfive-visionfive-2.dtsi
> > +++ b/arch/riscv/boot/dts/starfive/jh7110-starfive-visionfive-2.dtsi
> > @@ -390,6 +390,12 @@ spi_dev0: spi@0 {
> >  	};
> >  };
> >
> > +&syscrg {
> > +	assigned-clocks = <&syscrg JH7110_SYSCLK_CPU_CORE>,
> > +			  <&pllclk JH7110_PLLCLK_PLL0_OUT>;
> > +	assigned-clock-rates = <500000000>, <1500000000>; };
> > +
> >  &sysgpio {
> >  	i2c0_pins: i2c0-0 {
> >  		i2c-pins {